The serial number is often hidden and stamped on the other side, facing the keys).
On the front of the [b] action frame (after the keyslip is removed), or stamped on [c] of the cheek blocks, viewed to the right and left of the piano's keyboard.
Here are the TOP FIVE places to locate the serial number of your BABY GRAND or GRAND piano: (See this link for a detailed picture of where to look) Note: You may have to remove the (1) music desk first and then (2) gently clean out any dust from your piano's plate [using a soft dry cloth vacuum hose] before these numbers can be found. Located on the right, this acts as a 'bridge' to the 'beams' of the cast iron plate.
Serial number locations are found: 1) On the piano’s cast iron plate, near the tuning pins, as you face the keys. 3) On the piano's soundboard (see link above for a diagram).
2) Under the opened lid on the ledge, stamped on a little plaque, to the right or to the left.
3) Stamped on the back of the piano; near the top of the wood frame.
Pianos can almost always be linked to their respective year of construction according to their serial number.On older pianos, you may find 3-5 screws, underneath the keyslip, that will need to be removed (or, simply lift up, if no screws are present) to view the action frame.The serial number may be stamped on the front of the frame's wooden base, immediately under the keys.To find the serial number of your Steinway piano, look for a number (most likely between four and six digits in length) located on the lower part of the piano's cast-iron plate by the tuning pins. Steinway's model numbers are actually a part of the cast-iron plate, but each piano's unique serial number is stamped onto the plate.Because of this, sometimes the serial number, especially on older, rebuilt pianos, gets painted over or otherwise removed.
4) Printed on one of the hammers, found on either end of the piano (newer or imported pianos).