One of the first things we were told in the babies can sign classes was that when babies first try to sign they approximate it as best they can, so you need to keep an eye out as your baby might be signing sooner than you think.
Apparently, often the first one is clapping for “more” (hold your secondary hand in front of you, flat, palm in. Tap the back of it with your other flat hand, twice). It’s important however to continue to sign correctly yourself, even if the baby signs differently.
A parallel in spoken language acquisition is described by Berko and Brown (1960) as the fis phenomenon:
A child called his toy fish a fis.
A: This is your fis.
C: No, my fis.
[continues like this]
A: This is your fish?
C: Yes, my fis.
In terms of Polly signing, I probably get quite irritating to other people communicating with Polly, as they often learn the sign from her rather than me. This leads to a bit of Chinese Whispers (how do you imply that without the casual racism?) with them signing “shopping” to her instead of “bird”, “chat” instead of “milk”, or “helicopter” instead of “music” for example. I’ll often correct adults “no, the sign for bear uses claw hands,” where I wouldn’t correct Polly, just reinforce the correct sign while saying “well done!”
I note my own hypocrisy here with the irritation I feel when the kids on Mister Tumble are praised for their appalling approximations!
Some of Polly’s approximations are:
Signing “L” for “Mummy” (finger spelling MM is three fingers tapping your palm, L is one finger).
“Baby” and “bear” look almost identical except her bear involves tapping and her baby involves rocking. Bear should be claw hands on opposite upper arms, and for baby, the hands meet each other, or on the forearms.
“Bird” and “duck” should be signed in front of your mouth, but she doesn’t.
For “Cat” she uses a single pointy finger on each hand, not the two I use (four is also correct but I save that for tigers), and only moves them inwards, not out to represent whiskers.
She signs “monkey” completely upside down.
Berko, Jean & Brown, Roger. 1960. Psycholinguistic research methods. As described by Clark, Eve. 2009. First Language Acquisition (Second Edition), Cambridge University Press.