He is but that is not the reason for signing. Many reasons exist for signing as not everyone can read fast enough. If you notice the way signed programs go out its normally on the repeat or a later transmission, not on the original. The reason you are not allowed to hide these is because of the stupid way bandwidth is managed by Freeview, trading it off across the multiplexed channels. it would in reality be very easy to generate a signed graphic or real person and use digital techniques to mix it in or insert it. However AD and subtitles use little more bandwidth than a normal transmission and can be accommodated, signing has either to be part of the transmission or not, If it was separate, more bandwidth would be needed, costing more dosh, and more to the point reducing somebody elses bandwidth.
As I always said about digital TV, the system is run for pack em in get the dosh in to the people who run it, rather than make it have redundant capacity to allow for such extras as optional signing.
If your attitude to disability shown here is the same as in the real world, how you have survived so long eludes me! :-) Brian