Among the signs listed in WomanSavers.com, these are the ones I found really common or more applicable to situations nowadays. You just try to bug your mind thinking whether it's based on personal experience or not... :)
Cheater starts bringing you flowers and acts especially nice or cheater doesn't bring you flowers anymore and acts especially mean.
At the beginning of an affair, the cheater may actually be more affectionate than usual due to guilt feelings.
After the affair has been going on for a while, the cheater often starts finding fault with the partner as a defensive mechanism (i.e., to justify the affair in their mind).
Cheater's relationship with you will almost always change. They become more distant, fault-finding or blame you for their behavior.