After write operations, BIST schemes for RAMS relying on signature analysis must compress the entire memory contents to update the reference signature. This paper introduces a new scheme for output data compression which avoids this overhead while retaining the benefits of signature analysis. The proposed technique is based on a new memory characteristic derived as the modulo-2 sum of all addresses pointing to non-zero cells. This characteristic can be adjusted concurrently with write operations by simple EXOR-operations on the initial characteristic and on the addresses affected by the change.