Hey Lyndon,
I am unaware of an official set of icons, but you may want to review the API ToS [1] and the Branding Guidelines [2] within which cover the use of the RTM cow logo. I am sure if RTM granted you permission, they would be willing to provide you with the logos.
[1]
http://www.rememberthemilk.com/services/api/terms.rtm[2]
http://www.rememberthemilk.com/services/api/branding.rtm
Just wanted to give you a heads up.
Thanks,
Jason Emerick
The information transmitted (including attachments) is covered by the Electronic Communications Privacy Act, 18 U.S.C. 2510-2521, is intended only for the person(s) or entity/entities to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer.