Yes, you would first glance at the stowage in the cockpit to ensure it was empty, then check the seat to ensure all the pins were in before entering the cockpit., it is drilled into you, they can and do kill people.
RAF Germany was slightly different as the main gun sear was not installed on the ground on the Jags, something to be honest I could never understand, because it takes seconds to fit and remove, so in that case there would be one pin in the stowage.
When strapping in you would do a final check to ensure all the pins were in the stowage then hold up 5 fingers to show all 5 pins were stowed and wait for an acknowledgement.
Many moons ago they were moving an old gate guardian off the gate to refurbish it in the USA and the seat fired killing to guy on brakes, there was a worldwide alert and all gate guards were checked, several were found to still have live seats fitted!