re paying a reasonable license fee, I wonder if RSA would cash my check for (say) $10 if I wrote on the check that it was for a license for whatever they might claim on PGP.

RSA might try to cash such a check, but if their bank is smart they won't accept it. A check is not negotiable if it contains a condition. Negotiable means it can be bought or sold. If the check is not negotiable then it can't properly be processed by the check clearing house, since that would require a negotiation. Only if the check were drawn on RSADSI's bank would such a check be depositable, since then your order to pay is being made to the same entity which is receiving the check.

One wonders what they would do with several hundred checks.

Return them, I would suppose. Eric