Yes. It is a masonic keystone. After a little research, I contacted the Anderson Co., SC Masonic Lodge and this is the email I received:
"Royal Arch Masons date from the completion of the second temple by Zerubbabel, Anno Inventionis (A.I.) – “In the year of Discovery”. This adds 530 to the common time. The year 1851 becomes 2381.
What does HTWSSTKS stand for on a headstone?
When it comes to historic cemetery symbols, acronyms are used as a form of shorthand. There’s only so much room on a headstone, after all. (Speaking of acronyms, in an earlier post, I explained the surprisingly upbeat meaning behind the rather dire-sounding acronym, FATAL.)
HTWSSTKS is an acronym with connections to the Masonic Temple, specifically Royal Arch Masons. The letters stand for, “Hiram, Tyrian, Widow’s Son, Sent to King Solomon.” Of course, now we’re left wondering who the heck Hiram is!
As it turns out, all third degree Freemasons study the story of a man named Hiram Abiff (a.k.a. Hiram the Widow’s Son.) According to legend, Hiram was chief architect for the Temple of King Solomon. When bad guys tried to squeeze the secret masonic passwords out of Hiram, he valiantly refused to tell them. As a result, the bad guys killed poor Hiram. In Masonic teachings, Hiram’s story is held up as an example of loyalty.
So, when you see HTWWTKS on someone’s headstone, you know that not only were they a Royal Arch Mason, but that they made it at least as far as the third degree in that fraternal order!"
email from: anderson.york.rite@gmail.com
I hope this helps!!
~Elizabeth