13 signs you're underpaid

"It stands to reason, because for many, compensation is a concrete litmus test of how well you're performing and progressing on the job - and how highly you're valued," explains Lynn Taylor, a national workplace expert and the author of "Tame Your Terrible Office Tyrant: How to Manage Childish Boss Behavior and Thrive in Your Job."

According to a 2014 survey from Glassdoor.com, a whopping 39% of employees believed they were not receiving fair pay in their current job.

But it's hard for them to be sure.

"The topic of employees' salaries is well guarded by most companies, so it's not always easy to figure out how your pay compares to your colleagues'," says Taylor. "If you're willing to invest the time and research or look for the signs, however, you'll be better informed as to whether you should ask for a raise or walk."

Here are 13 signs you're paid less than you should be: