"I haven't been put here yet the Lord knows when. Joe. Arrived here at 7 p.m."
From the York Historical Society website, a little info about the Old Gaol:
"Until 1760 the Gaol was a prison for the entire province of Maine; it then served as a county jail until 1820. For the next forty years it continued to be used for the incarceration of local wrongdoers. The Gaol then served briefly as school, a boarding house, and a warehouse, and by 1895 it stood abandoned and in peril from neglect..."
Postcards from the early 1900's were very popular and plentiful. For the price of a 1 cent, or 2 cent stamp, they were used to convey all kinds of messages, from simple and humorous "wish you were here" kind of things, to notifications of a relative's impending death, telling the addressee he or she "had better get here soon." Sometimes postcards shared heartfelt expressions of love, or a request for money, as well - all no different than today, really. Punctuation and upper case was minimal...think of postcards as the "text messages" of yesteryear.
P.S. It's pretty likely "Joe" did not end up in the Old Gaol, and was probably just vacationing in York, in July. However, there is a list of many of the former inmates inside the Gaol - now a very fun and fascinating museum for all ages. Follow website link above, to learn more about all York's historic landmarks.