USB CABLE

I have a strang question . i actually own the following devices

asus zenphone

asus zenphone 2

asus fonepad 8

now i want to ask how can we differentiate between the usb cables of the above mentioned devices, as far as i can tell their are different alphabits written on the side of usb cable which is attrached with phone. like on one cable it is written D and on other it is written as L and on other it is writted F and rest is same

so how can i tell which cable belongs to which device


plzzz help guys