anagrams should be made a synonym of permutations, and we should additionally add string on a case-by-case basis
Presently, many anagram challenges are string already. Of those that aren't, they don't necessarily feel particularly string-focused (e.g. "write a program that outputs an anagram of itself" is not really string because "write a quine" is also not really string). Additionally, some anagram challenges have five tags more relevant than string already.
EDIT: I've done the additions of string; almost all the challenges that needed it had it already, and I tagged the few remaining challenges over the last several days (to avoid spamming the active list).
I've now proposed the tag synonym. If you have 1250 reputation and a score of 5 or more on permutations, you can vote for it here. Note that even if the other answer gets consensus rather than this one, we'll still have a record of which question was originally in which tag, so we'll still be able to implement it, and I haven't seen anyone argue for keeping the two tags entirely separate, thus the general concept of synonymising them seems to have consensus.