Landlord broke special clause in lease

I moved out 2 1/2 months early during my lease. However, I am still paying rent until a new tenant comes. There is a special clause in my lease that states all real estate signs and lock boxes will not be on the property. I had my own For Rent sign up to try to find a renter for the landlord (so I could exit my lease early). The day after I moved, the landlord had a real estate sign & lock box placed on the house. He also removed my sign. Is this enough to have the contract broken and end my obligations?

You could argue that yes, and even go to small claims if need be. He has to allow you to try to re-rent.