Green’s Dictionary of Slang

1. (Aus.) the dress circle of the theatre.

1900		Bulletin 20 Oct. 12/3: Mdme. Slapoffski, much petted by the Conservatorium clique, sat in the d.c. with Mrs. Pinschof [...] and party.
1905		Bulletin (Sydney) 2 Nov. 24/1: I’ll pay my bills – there are twenty-nine – and I’ll buy the wife new clothes, / In the d.c. row she shall far outshine the daughters of Isaac Nose.

2. (US Und.) a dangerous character.

1933

‘Goat’ Laven Rough Stuff 75: They [...] took us down to the cells, and threw us in for being d.c., that means dangerous characters.

3. (UK Und.) detention centre.

1989

J. Morton Lowspeak.

4. (US prison) the death cell.

1992

Bentley & Corbett Prison Sl. 105: D.C. also C.C. […] a security cell where the inmate is kept just prior to his execution, usually the 24-hour period prior to his scheduled execution time. This cell is called the ‘death cell’ or ‘condemned cell’ and is commonly known as the ‘D.C.’ or the ‘C.C.’.