i had a short cervix since 22 weeks pregnant and brown discharge the entire time. it doesnt mean anything really... if its blood red then you will know you are in labor. i ended up getting induced at 35 weeks pregnant. i was DONE! haha
It could be a bit of bloody show which is most definately a sign of labor and since you DO have a short cervix I would give the doctor a call just in case.
I would especially be concerned if it appears to have a mucusy like texture. Also if you haven't had an ultra sound to determine that you do NOT have placenta previa you need to call. And finally but MOST IMPORTANTLY if you and your DH have different blood types and you haven't had an RH factor shot that you most definately need to call. Sometimes when the baby has a different blood type than the mother the mother's body can start rejecting the baby in the 3rd trimester and it can be deadly to your baby.