I have seen a couple of these. One sold on auction recently for $575, and another is listed on Gunbroker.com for an opening bid of $995, but it has not yet had a bid.
Receiver
On the receiver
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/barrel
Look at the receiver
Receiver
Check the receiver and barrel
Receiver.
Receiver.
Check the receiver.
barrel, tang, receiver
Bottom of receiver