At the risk of unnecessarily complicating this discussion ...
to me, the lower part of the character looks too different from アン. The character that it most resembles to me is the 種字 for /khaṃ/ (in Japanese: ケン), which can be seen about halfway down this page:
神魔精妖名辞典:悉曇字母・種子対応表 On that page, the top part of the character (denoting the syllable final ン sound) is depicted with just a dot, but it can also be represented by a dot with a curved line underneath, as in the OP's image. According to that page, the /khaṃ/ character represents Dainichi Nyorai in the Womb Realm.
The reason I hesitated to post until now is that the /khaṃ/ character is close, but not an exact match, and it is also comparatively
quite obscure, making it seem unlikely that the OP would have come across it somewhere. If the OP can give more information about where the posted character was seen, that might help in accurately deciphering it. (It's possible that whoever created it was not very familiar with the Siddham characters, and made mistakes.)
Unless more information is uncovered, going with
@Majestic 's answer is probably the safest bet.