The Blackboard Monitor bit was a throw away remark Vimes made in response to his various titles - he said something like, I was also Blackboard Monitor when I was in school - or words to that effect. It backfired somewhat as dwarfs were horrified that someone would be proud to admit that they deliberately erased words that had been written.
In Thud, Vimes became possessed by the Summoning Dark. It controlled his body and nearly killed him in an effort to use him to seek justice when it had been summoned by the dying dwarf. It entered Vimes's body when he thought he scratched himself on a door. When Vimes had ultimately controlled the Summoning Dark and effectively threw it out, it left its mark on his arm. It isn't a tattoo, it's more like scar tissue.
In Making Money an army of golems was discovered and, somewhat like a nuclear deterrent, it was put to one side as a sort of threat to any other country that might decide to cause trouble with Ankh-Morpork. The golems were buried outside the city and were supposed to stay there by Vetinari's orders. Moist used the golems - got them to march across country and to support the weight of the tracks as the train went over the bridge that wasn't there. Hence Vetinari's comments to Moist at the end of the book.