My first choice is to look at the drip (bottom) edge - A mirror works well for this. Like Jerry said, you can often see the polystyrene (white foam board) and often you will see some plastic mesh ( the color of the mesh may also identify the EIFS system manufacturer) Those are indicative of EIFS. I also may remove the cover from an exterior receptacle. Tapping on the wall surface may give you a clue - I like to make sure. Another clue is that you may find buckets of material (stucco mix) somewhere on the property (garage). The material is usually left to perform repairs when required. The drip edge view usually works for me. Make sure you are looking at the main section of the wall - not the accents/trim areas.