Coil stamps are an interesting variation in US philately. They were issued in rolls rather than on sheets, and it will be immediately obvious if you have one because whilst they have perforations, two opposing edges will be straight.
Whether it's the top and bottom edges or the side ones which are straight varies, but it is unique to the coil design: stamp sheet corners may have two adjacent straight edges, and early stamps will have no perforations at all, as they required cutting with scissors.
1910-11 saw the release of a series of Washington-Franklin stamps in the form of coils. Of these the rarest was the coil sent to the Bell Pharmaceutical Company of Orangeburg, New York.
So far as anyone knows they were the recipients of the only roll of the deep violet rare stamps.
Now an exceptionally fine, used example of the Orangeburg coil stamps is going on sale at Spink Shreves, where a rare pair block of 1c blue stamps is also selling.
The stamp's violet colour is deep, and the stamp has much better centering than normally found, with a neat wavy line cancel of Orangeburg.
The piece is expected to achieve $11,000 by the end of the live section of the auction, but it has already had a bid of $4,750 over the internet. The live sale takes place March 12-14.