I saw the term 〇〇〇〇おじさん written in a chat profile. What does the 〇〇〇〇 mean?
〇〇 is used to mask/censor part of a word.
In contexts related to otaku-ish hobbies, Xおじさん is recently used to form a slang word that means "(stereotypical) middle-aged male X fan". The nuance is more or less similar to 大きなお友達. For example ガルパンおじさん (fans of Girls und Panzer) and アイカツおじさん (fans of Aikatsu!) are the two best-known examples of this, but there are other minor 〇〇〇〇おじさん's. Since there are exactly four circles and there is no particle between
おじさん, I feel he may be referring to either of these two works. Or else, he may be just implying he has some otaku-ish hobby.