If they are actually made AND ASSEMBLED in Austria, they will have Austrian proof marks on the frame, slide, and barrel. This is relatively rare to see in the US. About 10 years ago, Glock shipped a bunch of assembled in Austria guns here that were not originally made for the US market. As such, that batch has proof marks, and the Smyrna, GA import text is stamped on the bottom of the trigger guard.
US market guns are made in Austria, and shipped to GA, where they are assembled. These guns have little GLOCK logos in the places the Austrian proof marks appear on the non US market guns. The reason they say both Austria and GA is because they have to have the name and city of the US importer. So they are MADE by Glock GmbH, Austria, and IMPORTED by Glock Inc, Smyrna GA.
The 3rd category, MADE in GA guns, have USA on the slide, and little state of GA outlines instead of Glock logos or Austrian proofs.