Ours happened with one of the characters at Animal Kingdom.
Out youngest daughter is in the autism spectrum and was 7 years old at the time. She is verbal and and loves characters, so before we left for Disney I had printed off a bunch of autograph pages with the characters names and cartoon pictures to help her remember who she was looking for.
So many of the characters made such a fuss over these pictures - they really seemed to enjoy the fact that we had these. This was especially true of less familiar characters such as the stepsisters, princes, and other friends of main characters.
When we got to where King Louie was meeting children at AK, his handler told us that King Louie will pose for pictures, but he can not sign autographs. I think it is probably difficult for him to sign because he can't really move his fingers the way some other characters can.
My daughter was so excited to see him, she ran up to him and gave him a big hug and said, "Look King Louie I have your picture!" as she showed him the autograph picture page she had. I reminded her that King Louie wouldn't be able to sign the page, and then I stepped back to take her picture.
Louie signaled for me to come back to him and then tried to get the handler's attention. She did not know what he wanted, so when she came closer, he pantomimed signing the page. She said "It's ok Louie I already told them you don't sign." He kept signaling to her and then began pointing to our marker and then at his fingers. He did this several times and she said "Do you want to sign?" and he shook his head yes! She took the cap off and put the marker between his fingers like he way showing her, and sure enough he signed it for us!
I don't know if it was because he realized my daughter has special needs, if it was because she had shown him his picture, or if he just wanted to sign because she seemed to love him, so much, but he really made our day. She still talks about King Louie signing her book!
Kim