Hellboy: [Offering a beer.] Here. Drink up.
Abe Sapien: Oh, no, my body is a temple.
Hellboy: Well, now it's an amusement park.
In the first Hellboy movie, when they first show the BPRD headquarters, it reads "Newark, New Jersey". In Hellboy II, they show what is clearly the same highly distinctive building, but it now reads "Trenton, New Jersey".
When Hellboy hears Abe's music in the hallway, the display he is leaning against has Kroenen's mask from the first film.