Signing at age 4.
The infant began with the unmarked handshape "20", one of about five first unmarked handshapes typically used during the first two years of language acquisition from birth.
She first signed WATER at age 1;3 with the same handshape for a whole year before jumping to the "6" handshape at age 2;2. This long process is not unusual.
Interesting note: though the infant can touch her chin at age 1;2 for WATER, she couldn't reach her under-chin with the sign DIRTY at age 1;3 until age 1;8. Probably something to do with the elbow and orientation.