Indeed, the Grin logo is a smiley face with a M and W as eyes that stand for Mimble Wimble. The reason for this is that Grin is an implementation of the Mimble Wimble blockchain protocol.
Mimble Wimble is a blockchain design named after the Harry Potter tongue twisting spell from Harry Potter. Like this Harry Potter spell, Mimble Wimble blockchain stops the blockchains from blabbing and leaking personal information. Grin therefore has no addresses, and no amounts visible on the blockchain.
For more information of grin as a project, its best to visit the official grin website and to read the discussions on this forum:
https://grin.mw/
https://forum.grin.mw/
For more information about the logo, see the explanatory picture from 0xb100d or read the full discussion on the logo [Link]
