A nod seems to be the preferred salutation, here in Facist Britain. I've only ever seen a wave from an old boy on a vintage bike - very friendly. 'The nod' varies from 'Good to see you out today mate' to 'bah humbug, I can't be arsed knodding at you and your pesky Bonneville' (usually from pseudo-racers and up-themselves cruisers). When there are too many bikes around then most people tend not to nod, for reasons stated above.
Oddly enough though....just yesterday, whilst plodding along a dual carriageway at no more than the national speed limit

, I was pleasantly surprised to see a motorcycle cop coming the other way who gave me a 'Good to see you out today mate' nod! It did occur to me that he might just be trying to get rid of a wasp from his helmet. But for a moment, my worldy woes eased off and life in Old Blighty seemed a tad less...well, facist.