You can have a tribute to a deceased family member, friend, pet, whatever...just not sure it has to be visible for the 3 hours that you work for the week. Wear it in practice, around the house, out in the community...but it has to be worn while on TV?
Then someone will be upset that they cannot wear "tributes" for stuff like AIDS awareness, domestic violence, The Human Fund, all kinds of things. It is not that the NFL would not support it, but players will soon look like NASCAR cars if they can wear all these stickers, socks, gloves, etc.