The things about a mole that might alert to you that something suspicious is occurring are as follows
It has become sore or irritable or bleeds for no apparent reason.Usually this may only mean that the mole has been irritated by something external such as knock or rubbing or something that has been put on the skin.This type of irritation will usually go away within a few weeks. Sometimes if it is sore it may mean an infection is present and your doctor may need to examine the mole.Sometimes antibiotics may be needed
The type of irritation that may cause concern is if a mole recurrently or persistently stays irritable for more than two or three weeks.At this stage your doctor definitely needs to be consulted
Sometimes dangerous moles are not irritable,lumpy or bleed and they may be quite flat.
With this type of mole one has to rely on how it looks.Generally dangerous moles look odd even to the untrained eye.Many people will say they do not have the expertise to pick something that looks suspicious but this is not correct.
For example many people can pick someone acting suspiciously without having special training.This is the same situation with odd looking moles.Many people that develop melanomas at a site they can see believe there is something unusual about the spot.Do not ignore your own suspicions and seek a professional opinion.