In English, ‘sine’ (that is, the trigonometric function so-named) and ‘sign’ (as in ‘plus sign’ and ‘minus sign’) are homophones, and so in doing mathematics in English, we use the prefixes ‘trigonometric’ and ‘algebraic’ to distinguish them. In particular, the expression ‘algebraic sign’ is heard a lot. Now, how does ‘sign’ in the sense of ‘algebraic sign’ get translated into Esperanto? In spite of its high prevalence, it is tricky to track down its translation. Now, from the beginning, a native speaker of English would expect, given the offerings in the English-Esperanto dictionaries for ‘sign’, that the translation would be ‘signo’ (and, indeed, as we shall see, it is). However, if you’re cautious, you might seek confirmation, for example, in PIV. But – ho, ve! – PIV does not give any explicit indication that ‘signo’ can refer to the plus sign or the minus sign.

Searching around a bit more, we find that under ‘plus’ in Benson, ‘plus sign’ is rendered ‘plussigno’. Well, that nails it. We could stop there, but it is interesting to note what happens along another path, namely, being aware that there is such a thing as the ‘sign function’, and looking that up in Wikipedia, and then switching to the Esperanto version, where we see that the title is ‘signuma funkcio’. So, again, that nails it. An interesting aspect of this path is that Wikipedia, usually very good about redirecting near-hits to the relevant article, does not do so for ‘algebraic sign’. Indeed, Wikipedia has this long article – titled, as I said, ‘sign function’ – devoted to algebraic sign without ever once in the article explicitly containing the expression ‘algebraic sign’. So, Wikipedia’s performance regarding ‘algebraic sign’ is pretty poor too. An advanced student looking for a discussion of ‘algebraic sign’ would know to look up ‘sign function’, but a struggling Algebra 2 student looking for ‘algebraic sign’ would be left high and dry. So, Wikipedia is then left merely preaching to the choir.

Maybe this is interesting for you: http://dvd.ikso.net/vortaro/Matematika_vortaro.pdf
3148-3154 (signo) and 3156 (sigumo) and 3155 (signum-funkcio).

It remains difficult to find a translation in all specialized studies such as in chemistry, biology, physics, mathematics, ...
As a hobby I am magician and sometimes I find not even the correct translation for the various handles and actions with cards, coins, cloths, ... in my own language (dutch). So I have not started yet to look for translations in esperanto.