The Yoyo (M)'s have an internal 1/4" 20 UNC screw thread. This is the standard for most speaker stands and mounts. The internal thread is found on the bottom of the speakers.
As such if you wanted to secure these speakers to a wall we would recommend speaker mounts similar to OmniMount's 10.0 Wall and Ceiling Speaker Mount.
Please bare in mind that you will need to be able to reach the buttons located on the top of the speaker in order to operate and power the speakers on.