m 是mailing cash.

你是否在 E BAY 或拍賣網站見到？好簡單，mailing cash 是寄現金，即是把銀紙放在信封中寄去。乜有人咁做咩？

A similar policy applies to mailing cash as a payment option. Certain non-U.S. branches of eBay allow sellers to advertise wire transfers or mailed cash as payment options, provided such methods are not the only payment options the seller accepts.[21][22]

http://en.wikipedia.org/wiki/EBay

2006-12-06 10:52:28 補充：
點解咁簡單都無人答？

for economic world:
M is money

for sex education
M mean period.

i dont know which u referring