Unlike James, Sirius didn't have a broom of his own. His mother had taken it away for 'improper conduct' which probably meant she disliked his choice friends, and probably his attire ("Sirius Orion what are you wearing?! And your hair, oh Merlin above, cut your hair! You look so utterly common! You're a Black try to at least look like it!"), and his lifestyle, and everything he did in general. His broom was currently back at home, under lock and key, in his father's study but you can bet your bottom Regulus had his. Sirius planned on knicking it as soon as he could. He'd have to tell James about this at a later date.
Grinning a bit crookedly then, Sirius nodded his head in agreement before ducking into the school broom shed to borrow one for himself. "Hope it doesn't knock someone out like that cup did when we first tried that charm in class." Sirius said with a chuckle.