Green’s Dictionary of Slang

(US black) ritual handslapping that signifies a greeting or farewell.

1964		‘Return of Honky-Tonk Bud’ in D. Wepman et al. Life (1976) 69: ‘My dear hip friend,’ the letter began, / ‘Here’s some splow and a big shoddy-doo.’.
1970		G. Cain Blueschild Baby 33: J.B. leaps from the bench. ‘Hey nigger how you been. My man give me some splow.’ We swap fives.