Most of the answers here seem to be about what founder salaries should be, not how investors look upon salaries (which is what the question actually is).
The answer to the question is that investors are looking for a return on their investment, and founders salaries are one of many signals to investors about whether the company is poised to deliver a significant return. One of the reason that many incubators have caps on salaries is that the investors running those incubators generally believe that at a certain salary (or higher), a founder may be content enough with the income that he or she isn't "hungry enough" to grow the company quickly or effectively enough. So, explicitly: any investor who puts a cap on founder income is purposefully trying to use an inadequacy of income to drive behavior.
Not all investors are like incubators. If you bootstrap your way to a successful company, and you're looking for additional investment to help grow the company, than your salary may not matter at all. I'm pretty sure that a16z didn't care at all what the salaries were at imgur when they invested.
If you're pre-revenue, do not have significant adoption, do not have a significant moat, and you're an unproven founder, then the salary signal probably matters to most investors: if you show that you're starving yourself, and that you will really only be able to afford to live properly if the company is successful, then you're presenting a strong signal that your interests are strongly aligned with the investors. However, if you have some of those things (revenue, adoption, moat, previous successes), then you can likely be taking a decent salary for most investors.