Had to find my link to the regulations:
The full DOT code (with date) only has to be on one side. This side is supposed to be the "intended" outboard sidewall, but by no means is an absolute. There is no law that states the tire has to be mounted with the "intended" outboard sidewall for sure facing outwards.
Here is the link to the long regs, that is interesting reading for some people. it explains they way tire molds are made and why the full DOT code with date is not practical to be put on both sidewalls. It also give a lot of the history that went into the decision making for the way things are the way they are now:
Here is the link:
Tire Safety Information, Final Rule.
and here is an excerpt:
VII. Agency Decision regarding Final Rule
- A. Summary of Final Rule and Rationale
The final rule establishes a single standard for light vehicle tires, FMVSS No. 139, New PneumaticRadial Tires for Light Vehicles
.�The final rule contains labeling requirements that address the following aspects of tire and vehicle labeling: tire markings, the Tire Identification Number (TIN), vehicle placard content and format, placard location, and owner�s manual information.�NHTSA will also be establishing upgraded safety performance requirements for tires in a forthcoming final rule, which would also be included in the new standard.
The rule applies to all new and retreaded tires for passenger cars, multipurpose passenger vehicles, trucks, buses and trailers with a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 pounds) or less, manufactured after 1975, and to all passenger cars, multipurpose passenger vehicles, trucks, buses and trailers with a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 pounds) or less. 
� The requirements are summarized below.
NHTSA has decided that the size designation, maximum permissible inflation pressure, and maximum load rating must be placed on both sides of light vehicle tires.�The full TIN will be required on the "intended outboard side" of the tire and either the full TIN or a partial TIN, containing all aspects of the TIN except for the date code, will be required on the opposite side." "Intended outboard sidewall" is defined in FMVSS No. 139 as the sidewall that contains a whitewall, bears white lettering, or bears manufacturer or model name molding that is higher or deeper than that on the other sidewall of the tire.�If a tire does not have an intended outboard sidewall, the tire must be labeled with the full TIN on one sidewall and with either the full TIN or a partial TIN on the other sidewall.�Requiring that a form of the TIN, whether the full or partial TIN, be on both sides will ensure that important consumer information will be on the outward facing sidewall, regardless of how the tire is mounted.�Requiring that the other items of information be on both sidewalls will aid consumers in properly maintaining their tires and loading their vehicles.
NHTSA is making another change to the TIN.�The rule requires that each character in the TIN be 6 mm (1/4") high.�The agency believes that a requirement for a uniform TIN font size will significantly improve the readability of the TIN.