What is an icon or symbol that denotes 'automatic' ?

More details: Working on an application where there will be a list of bills, some with an actionable button inline that says 'Pay', and others are not actionable as they automatically are billed.

My options:
Disabled / grey type button that is labled 'Automatic'
Just a label that states 'Automatic'
Or an icon / symbol that denotes 'Automatic'

I will be testing all the above options, however I am stumped as to what type of symbol or icon could represent something that is going to be actioned automatically. Suggestions to this would be great.