Do you know the make of this BMX bike? Do you know the make of this BMX bike?  The only identifying mark is a stamped M on the rear of bike.

 Picture of frame stamped on trackend/dropout at right-rear of bike.
Surprisingly this is enough info to give a lead.

http://bmxmuseum.com/forums/viewtopic.php?id=1493 says 


"Mongoose used the M on the drop outs of their frames in the early-mid 90's"
"Mosh stamps their frames with an old english "m"."


So your next step is to start browsing through http://bmxmuseum.com/bikes/mosh/ and  http://bmxmuseum.com/bikes/mongoose/ looking for a match.  There are over 5000 bike photos to compare - good luck!

Mosh logo on Downtube - can't find a photo of one on a dropout though.