Abstract: A window assembly for use in mass transit windows has a frame, a windowpane sized to fit within the frame, a removable sacrificial glazing panel covering or protecting one side of the windowpane, and a self-locking seal assembly biasingly securing the removable glazing panel towards the windowpane without the need for screws, drills or welds. The seal assembly has a first interlocking arm provided with a locking lip, and a second interlocking arm with a receiving groove which is biased from its free position into a locking position in locking engagement with the locking lip of the first arm. Preferably the locking arms are unitary with the seal assembly. The locking arms may be disengaged and the sacrificial glazing removed and a new sacrificial glazing panel installed without removing or disassembling other components of the window assembly.