A transition altitude is set for every Terminal Control Area (TMA). The transition altitude is published on the IACs of aerodromes located within the TMA limits as also on the IACs of aerodromes located below the TMA when the minimum holding altitude is above the TMA base. The transition altitude is also published on the chart (scale 1:1,000,000) issued from the Aeronautical Information Service, for VFR flights, when the transition altitude value is different from 5000 feet. The transition altitude is never less than 450 m (1500 ft) above the aerodrome.
(French AIP ENR 1.7.2.2)
So when there's no specific transition altitude on your chart, you can assume that the TA is 5000 feet. Who told you 3000?