While the previous answers justify the reason for it not being there, you can find it. At least for ÖBB trains, head over to the Fahrplan (i.e. the Timetable). These can typically be found around the stations or on the platforms. You will find that every train, even the S-Bahn, has a unique Zug-Nummer (Train Number).

http://blog.belcl.at/data/Windows-Live-Writer/d3f9f594500f/6065EB4B/2012_05_23_Fahrplan.jpg

^{Source (Ignore the yellow circle. It just indicates the train does not operate on a certain day)}

While the previous answers justify the reason for it not being there, you can find it. At least for ÖBB trains, head over to the Fahrplan (i.e. the Timetable). These can typically be found around the stations or on the platforms. You will find that every train, even the S-Bahn, has a unique Zug-Nummer (Train Number).

^{Source (Ignore the yellow circle. It just indicates the train does not operate on a certain day)}