They must have learned more than just phrases because if you sign to a deaf person they sign back.
And now those people have some sign language they are not going to unlearn it, if they are people he encounters on a regular basis then they are going to continue signing.
I'm just about to derail, but stick with me.
Can I recommend a book? Lorraine Fletcher's 'A language for Ben', here's a summary of the bit that had me in tears.
In the mid 1980s Ben Fletcher was diagnosed as profoundly deaf, BSL was actively discouraged in education and families at this time. His mum Lorraine wanted her son to have as normal a life as possible but decides BSL is the best way forward.
She starts to learn BSL and also attempts to get Ben in to nursery. The nursery stall stall, how will they cope with a deaf child? Will it upset the nursery? What about the other children? Wouldn't he be better in a 'special' setting. Remember this is 10 years before the DDA.
The manager says they will let her know.
She doesn't have much hop and that evening sets off to her advanced BSL class determined that if Ben can't go to that nursery then she will find one that will take him.
As she walks down the corridor to her advanced class she notices the door to the beginners class is open, when she looks inside she notices the nursery manager in the class, then she notices the entire nursery staff are also in the class. She knows then that Ben has a place in nursery.