This is a well known countermark. It's still a maverick (unattributed) as far as I know. I have seen several of these over the years, always on Half Cents. They are a mystery, like so many other countermarked coins. "CTS" was a common abbreviation of "Cents" during the 19th century (seen in old newspapers). It could have been used as a trade token/check, or it could have been used for something else entirely.

Coincidentally, I just penned an article about counterstamps being used to "redenominate" coins; this, for future publication in the National Token Collector Association's Talkin' Tokens journal.

The gist of it is that the practice of elevating the denomination of circulating cents seems to have been an early Civil War era phenomenon, given the shortage of then circulating coins. A great many Civil War and sutler tokens, many being cent-sized, were assigned values exceeding one cent, too. Akin to tokens, these redenominated coins were, in effect, an I.O.U. The 1855 half cent, elevated to the value of of four cents, is a maverick, I believe.

The Schiller pieces, Indian cents dated 1860, redenominated to ten times their face value, are perhaps the best known examples from this class of counterstamps. Here are three other examples from my collection

Virtually all of the redenominated pieces I've seen have been dated during or near prior to the Civil War. Here's another CAMERON HOUSE piece; this one, dated 1860. Note that both the obverse and reverse are stamped with a 5. The reverse 5 was centered atop the ONE in ONE CENT.

It's been suggested by some that this hotel was located in La Crosse, Wisconsin, but that establishment wasn't built until 1879, when there was really no need to elevate the value of a cent to a nickel. Note that all of the CAMERON HOUSE pieces so far known exist on cents dated 1859 or 1860, the latest year. If my theory is correct, I've found a more likely candidate for this issue in Harrisburg, PA, and it was newly in business in 1859.