Okay, one last try...
It is not the piece of paper that make the unpaid internship legal. Regulatory agencies will look at the six criteria and the actual fact and circumstance pattern on a case by case basis to determine whether or not labor law is being violated. There is no statue or regulation that exempts internships from federal or state minimum wage or overtime regulations.
Signed agreements between the employer and the employee (or intern) are typically given very little weight as reliable evidence - it is the fact pattern that will be considered the most reliable evidence.
As far as college credit, there is no exception to the law allowed just because the �intern� receives college credit for the work performed.
As I previously indicated this has become a hot topic for the U.S. Department of Labor and for many states. The State of California can and does rule on the allow-ability of unpaid interns. The legal use of unpaid interns has been upheld in circumstances in which they are appropriate.
What is becoming a hot topic is when an unpaid intern is placed in a for-profit environment. And this is happening, colleges are placing unpaid interns in a business. This does not circumvent labor law. Employers have been found in violation of labor law for using unpaid interns in violation of the criteria discussed above. The consequences of this for the employer are dire (large fines and penalties can and have been levied against employers for this).
As the unpaid intern, you have little risk.
The employer on the other hand (if it does not meet the criteria discussed above) takes a huge risk if they are found in violation of the labor law.
BTW, you don't have to take my word for any of this, merely google "unpaid intership" and read.
