Three ways to remove those "decorations":
1: Report graffiti on your property to Graffiti Free Brooklyn by calling (718) 802-3777 or by printing out a consent form, filling it out, and mailing or faxing it to the Brooklyn Borough President's office.
2: Report graffiti to Graffiti Free NYC by calling 311. As of two days ago, owners of residential and commercial property no longer to have to sign a waiver granting the city permission to clean the building. Instead, after graffiti has been reported, the city will notify property owners that the graffiti on their property will be removed within thirty-five days. However, property owners do have the right to call 311 within those thirty-five days and say that they don't want the graffiti removed or that they'll remove it themselves.
3: Community-based organizations can get free paint and supplies through the Mayor's Paint Program. Print out the application form, fill it out, and mail or fax it, or call 311. The organization has to submit a waiver from the property owner before requesting supplies from the city. Call the Mayor's Community Affairs Unit at (212) 788-7418 for more information.