The arms were officially granted on January 9, 1956. 
„The T stands for the name of the municipality, as well as for St. Anthony, after whom the city is named. His symbol is the tau-cross (or T-shaped cross)."
Wappen der Stadt Tönisvorst
http://www.ngw.nl/int/dld/s/st-tonis.htm
UnknownUnknown  - constructed and added by Jürgen Krause