Called and hung up, left no message. Didn't register on caller ID.

Got call, didn't answer, but called them back. It was answered (lot of background noise; call center?).  When I asked who I was speaking with thy hung up.  

Have received several calls and messages from "Steve Martin". The other number was 650-752-8445. Both were automated identical messages. Called back and got voice mail with an error.

message said there is an enforcement action executed by US Treasury that required immediate attention it would be a federal offense.  same exact message from 6650-752-8445 number.  Others have written that this is a tax scam.

There is a fairly common IRS or "tax scam" being practiced by scammers on both Canadian and USA residents.
USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam

Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.

Educational post:
This scam is also described as scam #11, here:
http://phonehelp.2truth.com/facts_rev.html

Remember to return here, to 800notes.com, after you look at any of the information at that site, either to post more information, or to let us know you avoided the scam, or to read any further information about that number that others may post.