I'm a flight attendant in the US. Personally, I ask anyone who's using any kind of electronic device during take off or landing to turn it off. Why, you ask? Because my airline tells me to do that and they're signing my pay checks. Personally, I don't think your Gameboy or Walkman or camcorder is going to make us crash as the wheels go up, but my opinion doesn't matter when I'm at work. I'm just doing what I'm getting paid to do (hopefully in a tactful and kind manner). When we ask you to turn it off, just do it and don't argue. I myself, while traveling as a passenger, was scolded once by a South African Airways F/A for using my CD
player deep over the Atlantic and several hours after take off. I thought it was a silly rule, one which we don't have in the US, but I apologized and turned it off. Period.
As for deaf passengers, if we know they are on board we are suppose to offer them a briefing book detailing emergency procedures after they board. However, in this day of automated check in and self-serve everything, we don't always know a passenger is deaf until we're at their seat offering them something to eat or (more likely) drink. No, we're not signing during the announcements, but we are physically demonstrating the relevant equipment, and one would hope that anyone, hearing or deaf, could figure out what we're doing. Any safety videos shown, at least at my company, include captioning in English and Spanish. If anyone feels they need assistance, obviously we are prepared to help them, and all they need to do is ring the call light.
The bottom line is, if a crew member asks you to do something, including turning off the camcorder, please just do it.