Unidentified persons had blackened the face of Rahul Gandhi in posters displayed at Vijay Nagar Square and also used foul language against Congress and its 'hand' symbol.
After Congress workers learnt about the incident, they staged a protest at the bus stop.
Later, they filed a police complaint and demanded immediate arrest of those behind it.
Meanwhile, city Congress spokesman Shailesh Garg has announced a reward of Rs 11,000 to anybody who could provide definite information about those involved in the act.