There IS NO USPS regulation concerning "Any Soldier", however there is a DOD Postal Manual (DOD 4525.6-M) Issue #22093 dated 9 January 2003, which states, "a. Mail addressed to "Any Service Member," or similar wording such as "Any Soldier," "Sailor," "Airman," or "Marine"; "Military Mail", etc., is prohibited. Mail must be addressed to an individual or job title such as "Commander," "Commanding Officer," etc."
NOTE it says "...addressed to...
All of our addresses belong to real Coast Guardsmen
with the addition of an attention line, which is completely legal.
The real Coast Guardsman
is aware of and volunteered for this program, and uses the attention line as notification of what the package is for.
Some postal clerks get confused by this so we suggest to avoid any arguments you simply draw a line through the attention line. The Coast Guardsman will see this and appreciate your valor at the post office and he/she will still know what to do. We don't advocate getting into an argument with anyone.
The USPS FAQ is available online at http://www.usps.com/supportingourtroops/supportingfaqs.htm (which is not a regulation, nor does it reference any regulations).