In the pgf manual pgf_3.0.0.tds.zip, the $ signs in a few code samples display as pound signs £.
The first one is in the second code sample of "3.9 Adding Labels Next to Nodes" where an apparently intended label=above:$s\le3$ shows with pound signs instead of $ signs. (Looking at pgfmanual.pdf with either xpdf or katarakt.)
Not all $ signs are affected this way. It seems to be those which are in green "key=value" highlights.
The most recent compiled manual versions do not have the problem. Assuming it is fixed