Bea was informed her mother didnt wish to be on TV,
http://www.channel4.com/bigbrother/b...839471/view.c4
Whether she had prearranged that as a code for not going down too well with the public is open to debate. One thing for sure she will milk it to try and gain sympathy both in the house and with the viewing public.
Letters from home is a way of mucking with the housemates minds, they tend to mull over the messages looking for hidden signals. It can also weaken their resolve and induce homesick feelings in some.
It is of course open to abuse by any and all housemates, to have a predetermined series of codes. However BB being what it is they didnt know 100% that it would again be a feature this year.