+ AA6YQ comments below
Nope, that doesn't work. It returns no errors, just no entries. Typing RCC in the filter box and clicking the Tags buton returns 4 entries.
Backing up a step, I've got all the callsigns entered in the Callsign field and RCC in the Tag List field. Seems correct, it works with the pre-defined button.
+ Use this SQL expression:
TAGS LIKE '*RCC*'