TL;DR

While I never seen [ADMIN] be an acceptable term for ibis admins, you are correct. ibis.a are for us lowly admins who feed Zero's fetish fund (I am joking lol) and "ibis" is for clan members. Now using characters to surround the ibis tag is perfectly acceptable, as long as they are putting the ibis.a for admin and ibis for clan. this of course doesn't need to be followed if you go undercover to catch a hacker. Though using the ban command while no tag is. (correct me if I am wrong here).

While I have seen close iterations of the tag such as ISIS or the ibis steam group, I have never seen an issue with it as long as they aren't impersonating i.e saying the will ban/kick/slay you and such. However, I can see your thinking of how that could be misconstrued and in fact become an impersonation. I find it to be on a case by case basis.