I was on the Tube this morning and I spotted two boys having an apparently very animated conversation further down the carriage. They were late teens, in baggy jeans with a chain on the beltloop, big hoodies with the hood drawn up over baseball caps and waving their hands about in what looked like traditional gangsta rapper hand signals. I listened out for their voices, expecting some sort of glottal, South London incoherence but couldn't hear anything. Then I realised they were talking in sign language and were struggling a bit as neither had a hand free to hold on to something while the train moved.
Thought it was worth a comment: easy to make assumptions, eh?