Green’s Dictionary of Slang

1. an excited mood, a feeling of stimulation, intoxication (cf. down n.¹ ).

1938		F.D. Sharpe Sharpe of the Flying Squad 158: They regard it as a business, taking arrests as a little ‘down,’ and a good haul as a nice ‘up.’.
1999		K. Sampson Powder 334: He was loving every little bit of the adventure, and found himself on a permanent Up.

2. a prospective purchaser in a store [? they pick things up].

1942		Berrey & Van den Bark Amer. Thes. Sl.
1949		N.Y. Times 1 May 62: The hottest salesman who ever turned a looker into an up [OED].
1992		G.P. Pelecanos Firing Offense 43: At one point, when I moved to take an up, he stepped in front of me and threw an elbow into my stomach, keeping a wide smile plastered on his face as he greeted the customers.

3. (UK black) congratulations, praise; recognition.

2018-20

T. Thorne (ed.) ‘Drill Slang Glossary’ at Forensic Linguistic Databank 🌐 Ups - praise, compliments, recognition.