A combination lock and padlock combination as a lock is disclosed that includes a spring-biased pivot assembly comprising a locking dog and an engagement member; a push button pivotably disposed on the pivot assembly; a U-shaped shackle comprising a slotted leg for locking the locking dog; a spring-biased L-shaped catch assembly comprising a sliding member at one end and a tab projected from the other end; and a spring-biased opening warning assembly pivotably provided in the housing and comprising a locked mark at one end exposed at a window in a locked position of the lock and an open mark adapted to switch with the locked mark. Once the lock is opened by a key by one of a number of persons sharing the lock, the open mark is exposed on the window and other person(s) may be aware of same by seeing the open mark.