It is important to remember that when baby first attempts to sign back, they might not have the dexterity or coordination required to produce the sign the "correct" way- and that's ok! The goal here is improved communication and reduced frustration, not perfection.

However, you are the language model so I recommend that you continue to produce the sign the "correct" way (or at least a consistent way). Be sure not to copy-sign your baby's variation of the sign!

When my boys started signing back to me, I just let them produce the signs however they wanted. I never corrected their little fingers to match my sign. I accepted their sign for what it meant to them and as they became more comfortable with the signs, they eventually made those handshape corrections on their own.

IMPORTANT REMINDER:

When your baby attempts to sign back, you must respond appropriately! Tell them you understand them. For example, I remember the first time my oldest son, David, made the sign for MORE. He was sitting in his high chair eating blueberries and he started clapping. At first I thought he was just clapping. When I saw his face pinch together after I clapped back with him I knew he was frustrated that I was misunderstanding him. A moment later I realized he was trying to sign MORE. I confirmed his attempt to communicate by saying, "Ohhh- you want MORE blueberries" and proceeded to feed him another handful. His eyes instantly lit up and I could see his glee from being understood at such a young age. I believe it's very empowering for our children to have that. It makes them feel important.