Does anyone know what the "/r" in this score might mean?
Thank you so much...
This is actually tr, the notation for "trill," an embellishment (or ornament) on a note where you rapidly alternate between the main pitch and an adjacent pitch.
There are many different types of trills; the style of music (and perhaps editorial notes) will clarify exactly which type is intended.
You can check out more in the Wikipedia article.
Definitely a trill. A forward slash would be much taller, narrower and more slanted. Certain fonts leave the tail and the cross off the 't' almost entirely, especially when italic and bold. Below is a comparison of '/r' and 'tr' in a more standard, modern font (on the left) and an older, less common font (on the right).