Salem

When I add cash to the town bell a green number appears over my head. I can't figure out what does it mean

That is the free amount of Authority that is added to the bell. You get a roll for free authority each time you fill your bell based on the Law & Lore of the character who is filling the bell. You can think of it as the amount of silver you saved thanks to your L&L roll.

Oh, that's very nice. Must have missed it in the patch notes. I threw 264 silver at the bell and the number said 65, so pretty substantial bonus