You will be given a definition of a task first, then some input of the task.
In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].

The LAPD for searching for the person who tagged a police horse with graffiti this week - but the answer may be in the so-called 'art'. The horse, Charly, was patrolling Venice Beach with his minders on Tuesday when the vandalism incident occurred. It was broad daylight, and somehow the person managed to spray Charlie without the handlers seeing - a move that taggers pride themselves on, but usually with stationary objects and facades. 'I think it's unfortunate, but people love to tag things in Venice, so really, I guess a horse is just the next step,' local Mark Stegall told CBS LA.Charly was patrolling Venice Beach with his minders TuesdaySomehow a tagger managed to write 'RBS' and an arrow on his flankThe silver paint was easily cleaned offBut police want to find the person responsible and have appealed for help 
 Question:'RBS': The key to finding the tagger likely lies in deciphering the tag, _, and working out who it belongs to.
Output:
RBS