The Sticky Overflow, Q, flag can be set by certain multiply and fractional arithmetic instructions:

The Q flag is sticky in that, when set by an instruction, it remains set until explicitly cleared by an MSR instruction writing to the CPSR. Instructions cannot execute conditionally on the status of the Q flag.

To determine the status of the Q flag you must read the PSR into a register and extract the Q flag from this. For details of how the Q flag is set and cleared, see individual instruction definitions in the ARM Architecture Reference Manual.