WW2 Bomber crew signatures

I have been handed a BBMF brouchure dated 1986, the front cover has been signed by the following RAF aircrew. Could anybody provide details of these brave souls and advise if they are still around, and what was the reason for their signing. Also what, if anything, are these signatures worth ?

Bill Sykes – Liberator gunner 223 sqn
P.R. Bond – Lancaster bomb aimer 100 + 156 sqn
Jim Field – Lancaster rear gunner 49 sqn

John Lands
Bob Partner – 15 sqd
Don Thorn

The last three are indistinct so confirmation for them would be welcome

Paul