I’m certain this black and white image does not do the original (which I’ve not seen) justice as it is made from a digital image a microfilm copy of the 1803-1809 volume of estate inventories from Harford County, Maryland .
This image is of the right hand side of the index portion of the book. These letters form the tabs used to more quickly page to the desired portion of the index. They were not simply doodles made by a bored clerk.
Some of them are fairly difficult to read on this image and others apparently took some time to create. One is more likely to find items of this type in older records kept in bound completely blank volumes.
As long as the clerk didn’t get creative when copying the records. That type of creativity researchers don’t need.