I always find using an object as a reality check too narrow and chances slim to encounter it in my dreams. One thing I did find to be working is using colors as a reality check instead. For example- For an entire day when I think of the color blue or see anything that is blue, I tell my self "When I see the color blue I am dreaming. It is not real". I manage to get a wide range of objects and scenes that is related to the color blue (Navy blue, sky blue, blue-purple, etc) to be my trigger. So far it's working! Right now I'm training my self with the color green to widen my reality checks.

Thought this info might be helpful~ :3