Monkey Parliament is an unsigned poster from the Banksy Vs. Bristol Museum - Flags is an edition of 1000 unsigned on Chromalux (which is easily creased) - then you get into the signed prints which range depending on edition, age, rarity - and after all of that, you get the A/P's which are scarce and most of the time variants from the original signed editions as well as much lower edition numbers.

Hope that helps a bit.

(I am in no way presenting myself as any kind of expert, nor is this the definitive answer, but here goes...)

First off Monkey Parliament is a poster, I believe all of the expensive Banksys are prints. Posters are thinner paper, basically like a very nice photocopy, usually unsigned, usually in larger numbers or unlimited release. Prints are hand-made, with layers of color, some hand-finished, some silk-screened, paint, pen, etc...

As to signed vs. unsigned and edition size, basically it's supply and demand. An old unsigned print can fetch more than a newer signed one if the edition is smaller. Rarity is a big part of the market value.

And signed adds a big premium on top of rarity. I don't believe Banksy does unsigned prints any more, but many of the older ones are available in either version. With that in mind, a signed Trolleys can be worth a good bit more than an unsigned one, considering rarity plus signed. The image would still be the same, of course.

A/P = Artist's Proof