It really depends. Some mid-level design manager for Xbox signing this can't be seen as an Xbox or Microsoft endorsement.
Having Mike Turian, Executive Producer of MtG and Jason Tondro, senior designer for D&D at Wizards of the Coast, can for WotC, though. (Not to mention there are many other WotC/Hasbro signers too.)
If their company allows employees to identify themselves on a list like this with their employment, they endorse it.
It really depends. Some mid-level design manager for Xbox signing this can't be seen as an Xbox or Microsoft endorsement.
Having Mike Turian, Executive Producer of MtG and Jason Tondro, senior designer for D&D at Wizards of the Coast, can for WotC, though. (Not to mention there are many other WotC/Hasbro signers too.)