Does the mechanic involve the bicycle being stolen if it’s not locked?
I would totally mulligan this. If the bike is a ridable vehicle, I would write a rule that when the player exits the bicycle in a “lockable” location, this all happens automatically if the player is also carrying the bike lock.
Most likely unhelpful psuedocode...
a bicycle is a rideable vehicle. bicycle can be locked.
After exiting the bicycle when the player encloses the bike lock and the location is The Street with the Convenient Bike Rack:
now the bike lock is part of the bicycle;
now the bicycle is locked;
say "Good thing you have this bike lock with you. You lock your ride up securely in the bike rack. Those vagabonds won't be making off with your wheels this fine day!";
After exiting the bicycle when the player does not enclose the bike lock:
say "Someone will likely want to steal this sweet bike of yours. You should find something to lock it up with.";
After entering bicycle when bicycle is locked:
now bicycle is unlocked;
now the player carries bike lock;
say "You unlock the bike and swing your leg over, ready for an aerobic workout disguised as transportation.";
Instead of unlocking bike lock or unlocking bicycle when the bicycle is locked:
try entering bicycle.
Instead of locking bike lock or locking bicycle when the player is on the bicycle:
if the player does not carry the bike lock:
say "You wish you had something to lock the bicycle securely with.";
try exiting the bicycle.
Every turn when the player cannot touch bicycle and bicycle is not locked:
if a random chance of 1 in 4 succeeds:
move bicycle to Bicycle Thieves Den.