It depends on how the employee is signing.
If the employee jumps into a conversation with a comment like, "Hey! I know sign language too! Watch me! *fingerspelling something random*"... then it would be annoying and disrespectful. However, if the employee simply said, "Thank you." or "Have a nice day." in sign language... then that would be nice. I prefer to keep it simple and sweet.
Having a hearing person (or a deaf person too), that is a stranger, jump into a deaf person's signing conversation is disrespectful and annoying.
What do I mean by "deaf person"? Well, here's an example...
I was at a Denny's restaurant with a few deaf friends. While we were sitting there and waiting for our food, this deaf guy sees us signing and immediately approaches us. "Hey, you all deaf? Awesome! I am deaf too! Did you go to RIT/NTID? Wow! I graduated from NTID years ago! Cool!" He starts rambling on and on about how he used to be at NTID and how he knows all these deaf people in the area. Our food arrived and we didn't want to disrespect a person who was talking to us. So, we didn't eat right away. He kept talking and talking. Luckily, his mother interrupted him and said that he should leave us alone so that we could eat. He finally left. Just when we finished eating, he bothered us again with how he's deaf and we're deaf. Jeez...
