The ARRL does not make a method for us to detect if a call sign is a current member of the ARRL.
We have contacted the ARRL numerous times regarding this issue, and we have been constantly told that the information is private. We do find this argument to be incorrect as the ARRL does request Amateur Radio clubs to take payments on behalf of the ARRL and to become agents and to represent that ARRL. Furthermore, the ARRL requires that clubs maintain at least 50% membership in the ARRL to be recognized as Special Service Clubs but will not let clubs know who is a member and who is not in order to keep the special designation.
You must ask your membership every year to update their ARRL status. We recommend using a member editable skill and have your members login and update the skill. We already know that club participation to keep this information up to date will lack any clarity and we also understand that doing this requires a bunch of time on behalf of the club. The ARRL does not seem understand nor care. Please contact the ARRL if you wish to attempt to change their minds. HamClubOnline offered to enter into a non-disclosure agreement or other legal instrument.
Continuous e-mails to ARRL have gone unanswered.