What was found
(CAN) DURING FLIGHT, MODERATE RIME ICE WAS REPORTED AT FL 180 (-18C), WE STARTED ACCUMULATING ICE, REQUESTED A DESCENT TO FL 160. IN DESCENT, STARTED GETTING SOME PROP VIBRATION, 1050 RPM WAS SET TO AID SHEDDING. ACCUMULATION WAS MODERATE BOOTS EASILY KEEPING UP, SET ON SLOW, PROPS SET ON BELOW -10C. AFTER 5 TO 10 MINUTES FA CALLED, ADVISED WINDOW, SEAT 2E EITHER HAD CRACK IN IT OR A STREAK OF ICE ACROSS IT. PILOT CHECKED PRESSURIZATION, IT SHOWED NO INDICATIONS OF A LEAK. THERE WAS A PLEXIGLASS COVER ON OUTSIDE OF WINDOW THAT HAD A CRACK IN IT NOT ACTUAL WINDOW, SINCE ICE STRIKES ARE COMMON THERE AND FUSELAGE IS BEEFED UP. AFTER CHECKING ON THE GROUND IT WAS OBVIOUS IT WAS THE WINDOW. MAINTENANCE NOTIFIED.