Is it possible to mention an attachment when you are adding comments/activity just like you can mention other members and cards?
When you change anything in a card it is automatically shown as an activity.
There isn't a way to specifically mention an attachment, but you can mention a member anywhere by using @MemberName. So you can just say something like:
@John Doe, check attachment WireFrame.Jpg
@John Doe, check my last activity (being that it was the attachment)