Home for the Holidays - S11-E1
Other mistake: Only one set of prints were said to be on the garrote but in the last episode of season 10 Graham handles the garrote before handing it over to the murderer without wearing gloves. So there should have been 2 sets of prints.
Answer: It's certainly a personal choice about using one, and probably similar to how some people refuse to wear a helmet or forego other safety equipment. Most bells and horns on bikes are not very loud and probably wouldn't be heard in busy traffic, making them mostly ineffective. Murdoch would likely still yell, even if he had a bell or horn.
raywest ★