It may not be the same in all states, but the states (in the Midwest) where I am familiar with the rules and statutes specify that for a PE to seal a plan or drawing, they MUST be involved with the design from the start and oversee the creation of the drawings and plans. That is not to say that they have to do all of the work but they must have "responsible charge" of the work and oversee the person who does the work. Simply reviewing plans and stamping them is not responsible charge, even if you recreate every single calculation. Now, that said, it happens every day in every one of those states and some people never get caught. But if someone finds out and turns you in to the board, you risk losing your license.
JAE's comment that a PE seal is not required for residential homes is also valid in these Midwest states. Single family dwellings, whatever size are exempt from PE requirements.
The moral of the story is to check your state laws and be sure you understand all that is required before you proceed.