(I don't have enough reputation points yet to comment, so I'll make this an answer instead. Will convert to comments on other answers later, or to edits on other answers, once I have enough cred to ask those answers' authors whether they welcome the edit.)
I don't see any convention specified in either the "Concise Dictionary of Music" (Wm Collins Sons) or the "Essential Dictionary of Music Notation" (Alfred). Seems like you're on your own to come up with an approach that works best for you. As pointed out in the answer from @Tim, if you're already using staves, then why not jot out just those notes that are pushed, tying them to the downbeat chords to which they push?
Or if you want to go with chord notation, maybe just use that same "Ant." abbreviation that you saw in the examples given at http://www.musicarrangerspage.com/1493/how-to-use-anticipation-in-music/, not as markings on written-out notes in the staff as they do there, but as stand-alone markings prior to the anticipated chord, e.g.
Bb Bb Dmi ant. Bb