The most recognizable smell is the scent of coffee.

This is according to a scent recognition study conducted by Yale University in which 200 people were asked to identify 80 common aromas.

The top 20 most recognizable scents are as follows:
1. Coffee
2. Peanut butter
3. Vicks VapoRub
4. Chocolate
5. Wintergreen oil
6. Baby powder
7. Cigarette butts
8. Mothballs
9. Dry cat food
10. Beer
11. Ivory bar soap
12. Juicy Fruit gum
13. Orange
14. Cinnamon
15. Lemon
16. Tuna
17. Banana
18. Crayons
19. Cheese
20. Bleach
(source)