In PAYDAY: The Heist, you may find weird names on name plaques or the like. This was during Overkill's "Lucky 200" event where the first 200 people to show proof that they reached the max rep level of 145 would get their names in the game.
In a similar vein, the Counterfeit secret event resulted in two plaques on the walls of the secret vault that have the names of players that contributed to the event in some way.
Artist Disillusionment: Came very close on more than one occasion. When the secret in the first game was revealed, flame wars broke out and people also bashed Overkill for making the event too hard. Overkill responded by saying they may have to think about how they will interact with the community in the future, but everyone on both sides cooled off and everything was resolved.
Easter Egg: A small sign near the entrance to the gym in Mallcrasher in Payday 2 lists off several perks of joining, such as the first month being free. The fourth? "Another Selling Point".
Fan Nickname: "Old" or "British" Hoxton from PAYDAY 1 to differentiate from the current Hoxton that is in PAYDAY 2. The old Hoxton references himself Old Hoxton in the Christmas album as well.
Mean Character, Nice Actor: Hoxton in the first game is an Evil Brit who will yell at civilians at the top of his lungs while killing cops in cold blood and swearing at them in British profanity. Pete Gold, the voice actor behind British Hoxton, is very down to earth and actually tries to not swear in real life due to him having a child. Pete Gold, who wasn't called back by Overkill to voice Hoxton in the sequel, was actually surprised and humbled to hear that fans loved his take on old Hoxton so much that they created a petition to get him back for the role. Pete has even recorded several quick lines under the Hoxton persona for fans that requested it.