Modern postmarks and cancellations look like this

From the beginning of the use of postage stamps inthis country in 1847 and for sometime before—the"stampless cover" period—the postmark portion of thecanceling device has been almost always of circular shape.Sometimes the postmark and the canceling device wereganged together in one instrument. Sometimes they weretwo separate instruments. Sometimes, for convenience,postal clerks would bind the two instruments together.In any event the general idea has been that the postmarkshould fall somewhere on the envelope so as to be read-able. Often the clerks would make the postmark performthe double duty of canceling the stamp and serving as apostmark. Often early nineteenth-century postmarks con-tained only the name of the town and the abbreviationfor the State. And, as we have seen, some postmasterscut fancy designs upon corks to "kill" the stamps. Suchdevices, whether of specific design or only the circularends of the corks, are called "killers." Only fancy-shapedkillers are prized by collectors.