As an employee, it's not the federal government you'd worry about. It's your own company's lawyers, etc. You're much more likely to get in trouble internally for violating the company's policies about making statements related to the stock valuation than any outside entity.

Employees at Google (and many other tech companies) are often privy to what would be considered "inside information" about the company's future plans and performance. Making statements about the stock price's relative valuation can be seen as a form of making tips based on that material non-public information. It's not a good idea to go around making statements (positive or negative) about the current valuation.

"You're much more likely to get in trouble internally for violating the company's policies"

So is there a specific policy in writing regarding what you can and can't say? The issue certainly isn't revealing non-public information of a specific nature which is fairly obvious to keep under wraps.

I believe what matters is the amount of specificity. For example you can't say "Our earnings will be up this quarter so buy the stock". But you could say "I think we are doing well so I am buying the stock". Salesman, selling a product for a company, say, airplanes for Boeing are definitely able to make general sales like statements that could or could not be interpreted as a stock buying signal.

It's hard to make any kind of statement about the value of a stock without making an implied statement about future performance, given that most of the value is based on expected future outcomes.

Generally, the employee handbook of any public company will explicitly forbid employees from making statements that connect to either future performance or other major non-public info such as products or hiring. (If for no other reason than to protect the company itself from accusations that it's letting its people "pump" it's stock.)