Q:

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

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.

A:

A circular arrow - the same icon that most web browsers use to indicate Refresh. You'll also see this icon used on Calendars to indicate a recurring event and some online banks will use this icon to indicate a recurring payment/bank transfer. 

from: http://www.defaulticon.com

