Yes, you have come across one of those print signs that can be misinterpreted unless you dig deeper. When in doubt, look for clues in the surrounding text regarding the function of the sign. (Or Ask An Expert! Not just here, but you could ask a math or science teacher or scientist as well.)
In your example, the sign (that looks somewhat like a "pinch bug" or earwig to me) is a sign of comparison, indicating that radiation is proportional to (or "varies as") distance ("d") in the ratio expressed (one over d-squared). In your transcription, use the comparison symbol listed in Rule XX of the Nemeth Code on page 136. (456, 123456)
In the UEB with Nemeth lesson material, the symbol is introduced in Lesson 6 (6.7.15) and compared with the Greek letter alpha in Lesson 13 (13.7). You can reassure yourself that this sign is not the Greek letter alpha by looking to see if there is a definition for alpha nearby. Is alpha defined with a certain value, for example? Or are alpha particles under discussion? Is there such a thing as "radiation-alpha"?
Thank you for sharing this example.