One of the benefits that I have enjoyed over the years as a writer for Barr’s and other postcard periodicals is the letters and e-mails that I have received from postcard collectors from all over the world.  Last week, an e-mail arrived from Sophia J. in Buffalo, New York.  Sophia had purchased a striking Fourth of July postcard at a local show (Figure #1).  She asked about the meaning of the letter and number that appeared in the postmark on the back of the card (Figure #2).

Sophia, here is what I can tell you about the postmark on your card.  This postmark was made by a machine, specifically a machine manufactured by the International Postal Supply Company of New York.  The postmark has a round dial which indicates the city in which the card was posted (Springfield, Ohio), the date (July 4, very appropriate for this particular postcard), the time of posting (10 AM) and the year (1909).  The killer (that part of the postmark that cancels the stamp) consists of seven wavy parallel lines embedded in which is the number “1” and the letter “C.”  The “1” indicates the designated number of that machine in the Springfield Post Office.  The “C” means that your postcard was collected from a mailbox outside of the main post office.

To give you a little more information about the International Postal Supply Company, it began selling machine cancellation devises in 1888.  Their machines were trustworthy and sturdy and were soon in use by post offices across the United States and later Canada.  International produced many different canceling machines which used many different dials and killers your wavy line killer being a very common one.  The machines were sold with interchangeable metal numbers and letters for use in the postmark killers.  Figure #3 shows a card mailed in Chicago in 1907 with the number “17” in the killer.  This indicates that at one time, the Chicago Post Office had seventeen International canceling machines in use processing mail.  I would be interested in hearing from any machine enthusiast who has a number greater than seventeen in their collection.

On occasion, the numbers and/or letters would become loose and fall out of their machine.  That is the case with the card shown in Figure #4.  This card was posted at the Madison Square Station in New York City in 1906.  Although the “C” was still in place, the number had either fallen out or had not been inserted or reinserted into the machine.  Such “blanks” while not rare are nonetheless very collectible.

Four different letters are seen in International wavy line killers and each indicates a different service supplied by the post office.  These letters were “C”, “D”, “R” and “T”.  Figure # 5 shows a postcard sent from the New Kensington, Pennsylvania, Post Office in 1911.  The letter “D” in the killer indicates that this card was directly deposited at that post office rather than being collected from an outlying post box.

The letter “R” was supposed to be used as a receiving mark indicating the time and date that a card or letter reached its post office of destination.  However, postal clerks were not always fully attentive to these rules as is shown in Figure #6.  This card was posted from Mitchell, South Dakota, to Prairie City, Iowa, in 1909.  Mitchell, South Dakota, was clearly the post office of origin and not the post office of destination.

Another misuse of killer letters involved transit markings.  The letter “T” was designated as a transit mark to be used by any post office that processed mail during its journey between the originating post office and the post office of destination.  Figure #7 shows a postcard sent from Newark, New Jersey (post office of origin), to Millington, New Jersey (post office of destination) in 1910 with no intervening post offices in between.  The Newark postmark bears a “T”, a transit mark, and not the proper “C” or “D” designation.  Another example is shown in Figure #8.  In this case, the post office of origin was Mechanicsburg, Pennsylvania, the post office of destination was Pine Grove, Pennsylvania.  Since Pine Grove was a small town, the card first went to the Harrisburg, Pennsylvania post office for processing where it should have received a transit mark “T”.  Instead, killer letter is an “R” which was simply a receiving mark supposed to be used by the post office of destination.

If you’re wondering why the Post Office Service used so many different types of markings on a single piece of mail, the answer was accountability.  Each post office that handled a piece of mail was responsible for processing that mail in a safe and timely manner.  The various postal markings were documentation that the proper services had indeed been provided.

Sophia, I hope this has addressed your question about the meaning of the numbers and letters in your postcard’s cancellation.  If anyone else has a question about a card’s backside or if you have a card that you would like to see featured in a future Backsides column, please contact me at  Until next time, good hunting!By CH