Anything that is the recipient of the action defined by the transitive verb (in this case anonci) must take the accusative ending (unless it is a prepositional phrase)

In "Mi vidis la domon, kiun oni anoncis en la ĵurnalo", the house is seen by me, and 'they' advertised the house (represented by 'which').

I can also say "Mi vidis la domon, kiu estis anoncita en la ĵurnalo" == "I saw the house, which was advertised in the paper." In this case the house is not the recipient of an action, so no -n.

A clearer example is:
"Mi vidas la viron, kiun li batis per batilo" == "I saw the man, whom he beat with a bat"
"Mi vidas la viron, kiu lin batis per batilo" == "I saw the man, who beat him with a bat"

In the first case I saw the man who was being beaten by someone else, and the second I saw the man who was doing the beating. I highlighted each subject in bold and direct object (DO) in bold underline.

In this example, English also supports the suject/DO difference by the use of "who", "whom", "he", and "him". "Who" can only be used to represent the subject, and "whom" is used to represent the direct object. This is also the case with I/me, she/her, he/him, we/us, and they/them; Esperanto just extends this idea in general with the accusative.

If we didn't have a strict word order, I could say "I see her" and "Her see I" unambiguously (also "Me sees he", "Them sees she", ...).

I hope this helps.

Thanks for all the help.

Although the answer to the OP's original question is clear cut, there can be cases in Esperanto where it is not so certain as to whether to tack on the 'n' or not.

La kapon li ĉiam tenis turnita al mi
La kapon li ĉiam tenis turnitan al mi

Or following Zamenhof:

La kapon li ĉiam tenis turnite al mi (quoted in PAG).

Again there is a subtle difference between:

Li sendis sian filon Jakobon en la dezerton
Li sendis sian filon Jakobo en la dezerton.

Or,

Mi rimarkis policanon atendantan antaŭ la domo.
Mi aŭdis infanojn kriantaj en la apuda ĝardeno.

The essential thing to remember is that 'n' is there to make distinctions, to mark how something relates to the other elements in the sentence. It will often disambiguate.

sudanglo:Although the answer to the OP's original question is clear cut, there can be cases in Esperanto where it is not so certain as to whether to tack on the 'n' or not.

La kapon li ĉiam tenis turnita al mi
La kapon li ĉiam tenis turnitan al mi

Or following Zamenhof:

La kapon li ĉiam tenis turnite al mi (quoted in PAG).

This one seems similar to the "He painted the house red" vs "He painted the red house" ("Li farbis la domon ruĝa" vs "Li farbis la domon ruĝan"). In the first one he held his head turned, while the second he held his turned head. The accusative replaces our changing of the word order. I do like Zamenhof's more general 'turnite', though.

sudanglo:
Again there is a subtle difference between:

Li sendis sian filon Jakobon en la dezerton
Li sendis sian filon Jakobo en la dezerton.

Or,

Mi rimarkis policanon atendantan antaŭ la domo.
Mi aŭdis infanojn kriantaj en la apuda ĝardeno.

The essential thing to remember is that 'n' is there to make distinctions, to mark how something relates to the other elements in the sentence. It will often disambiguate.

I'm not sure what to make of the first example here. They are in each case non-restrictive clauses, since "Li sendis sian filon en la dezerton" makes perfect sense on its own, so my guess is that the non-accusative here is something like our English use of commas: "He sent his son, Jacob, into the desert.", because the lack of accusative emphasises Jakobo more than filon. With the accusative, Jakobon is less emphasized in respect to filon, just like in "He sent his son Jacob into the desert." without commas.

Again, my 2 cents, I don't know if that is the official interpretation or not.

I gauge the last two examples as the same case as the red house/house red example. "I saw the waiting policeman..." vs "I saw the policeman waiting", "I heard the infant crying" vs "I heard the crying infant". I'm not certain, but I think these generally only come about with transitive verbs.

I'm not sure what to make of the first example here. They are in each case non-restrictive clauses, since "Li sendis sian filon en la dezerton" makes perfect sense on its own, so my guess is that the non-accusative here is something like our English use of commas: "He sent his son, Jacob, into the desert.", because the lack of accusative emphasises Jakobo more than filon. With the accusative, Jakobon is less emphasized in respect to filon, just like in "He sent his son Jacob into the desert." without commas.

Again, my 2 cents, I don't know if that is the official interpretation or not.

I took the first example to mean "He sent his son, Jacob, into the desert." whereas the second, lacking the accusative, would mean "He, Jacob, sent his son into the desert." I'm pretty new to Esperanto so I'm not sure if that's how it'd work, though.

coderiferous:

I'm not sure what to make of the first example here. They are in each case non-restrictive clauses, since "Li sendis sian filon en la dezerton" makes perfect sense on its own, so my guess is that the non-accusative here is something like our English use of commas: "He sent his son, Jacob, into the desert.", because the lack of accusative emphasises Jakobo more than filon. With the accusative, Jakobon is less emphasized in respect to filon, just like in "He sent his son Jacob into the desert." without commas.

Again, my 2 cents, I don't know if that is the official interpretation or not.

I took the first example to mean "He sent his son, Jacob, into the desert." whereas the second, lacking the accusative, would mean "He, Jacob, sent his son into the desert." I'm pretty new to Esperanto so I'm not sure if that's how it'd work, though.

Hmm, I think you are right. That follows the definition of the accusative much better. I would say that the placement of Jacobo is unfortunate if that is the intended meaning, since it is so far from the 'he' it is associated with. But it is still unambiguous thanks to the accusative (unless you over-think it as I did).

At any rate, thanks to sudanglo for giving us such illustrative examples.

I do like Zamenhof's more general 'turnite', though.

So do I. PAG criticizes this however as it contravenes the general principle that participle adverbs should relate to the subject. But where the meaning is obvious, ie the participle clearly doesn't relate to the subject, I don't see why one should have to observe this stricture.

Li sendis sian filon Jakobon en la dezerton
Li sendis sian filon Jakobo en la dezerton.

For me the difference is the first means he sent Jacob (who was his son, or one of his sons), whilst the second means he sent his son (who incidentally was called Jacob).

sudanglo:

Li sendis sian filon Jakobon en la dezerton
Li sendis sian filon Jakobo en la dezerton.

For me the difference is the first means he sent Jacob (who was his son, or one of his sons), whilst the second means he sent his son (who incidentally was called Jacob).

In that case, in the sentence with the no “n” Jakobo, it would be better with a comma to clarify.

Li sendis sian filon, Jakobo, en la dezerton.

Anyway the sentence hasn’t a real difference in the meaning. No doubt Jakobo will die in the desert. XD

Ĝis, Novatago.

sudanglo:

Li sendis sian filon Jakobon en la dezerton
Li sendis sian filon Jakobo en la dezerton.

For me the difference is the first means he sent Jacob (who was his son, or one of his sons), whilst the second means he sent his son (who incidentally was called Jacob).

Hmm, I guess I was on the right track after all. I do like codiferous' interpretation, since it would be more general, but I suppose word order should suffice.
"Li, Jakobo, sendis..." for describing the subject.