How can you tell if there is complications with a mesh that was implanted for a femoral hernia?

Depends: Depends on what complication you are talking about. Infection would have redness, pain and/or drainage. Recurrence would be the hernia coming back. Sounds like you should make an appointment with your surgeon.

Obvious: There could be pain from a trapped nerve, a recurrent hernia, or an infection leading to swelling, redness and warmth.