Symbols on Banksy gift prints, by jusdeep on Jan 26, 2014 9:27:36 GMT 1, There are threads on here somewhere on the subject, you just need to do a search.
From what I remember from a few years ago, mostly speculation and guesswork with a smidgen of historical fact, but nothing concrete as to why.

Here's one on the Lincoln piece on cardboard:
www.flickr.com/photos/jeyku/5446119388/

CND (Peace), @banksy, Love and the cross and dots.
These dots appear on other prints in forms, not sure if they have the same symbolisation or meaning.
I can remember Roman or Saxon coins having this mark .
Also an ancient symbol in Buddhism… so maybe Mr B is a buddhist, or just plain godly.