"Watch" is subjective ... you can view, but not be involved in almost every airport. They encourage you at IAD, for example, to leave as soon as you drop your bag. This is something I ignore (and actually, they would send my bag to the no view area downstairs but I prefer to carry it over and watch the scanning process) and stick around to watch until my bag goes down the chute with the TSA sticker attached. You can be obvious enough to let them know you are there and watching if they do choose to open your bag, but you can't touch it, repack it or be involved directly -- it's part of TSAs arrogance and stupidity at work. If my stuff is seriously abused (it was once) when repacked, I catch the names of the TSOs and place a complaint - that is all any of us can do -- they control the status/shape of the bag when it is sent down the chute to the airlines, not us even when we can observe their process.