Anyone know this serial #?

[Diamond Dogg]

Can't post a pic right now, but it looks like a 1950's Columbia if I were to guess. Cantilever frame. Has a headlight. Serial number(s) are as follows: Top line reads: M.D. R224x51. Bottom says: 552622. The head badge is square, but you can't read anything off of it. I've been searching all morning and getting frustrated. Please help if you can. Thank you for your time...

[deorman]

If it's a Columbia it was badged as something else. This sticker is as close as it gets to square.

Also, their serial #s only have a single letter prefix