Yes, on certain models. Around serial number 1600000 and beyond.
It means that it is a Model 1890 (90) receiver. When Winchester introduced the Model 1906, they used the exact same receiver and action as the Model 1890, with exeption of the cartridge carrier. To readily differentiate between the two, Winchester stamped an "A" on the Model 1890 receiver and a "B" on the Model 1906 receiver. Bert H.
Receiver
On the receiver
This firearm has benn overhauled at the Winchester factory and a different receiver installed. James Friend
Check the receiver.
Receiver.
Receiver
Receiver.
It will be stamped into the side of the receiver.
Bottom of the receiver
Bottom of receiver
Check the receiver.