Correct usage of 「您是指？」
It is used when someone uses some pronouns like 这件事 or 那间房子 or else to refer to something, which is not definite enough for the hearer to figure out which entity exactly the speaker is referring to. For example:


  我很欣赏您的那幅作品。 I really appreciate that piece of yours.
  
  您是指（哪一幅）？ Which one exactly are you referring to?
  
  画了三匹马的那幅。 The one of three horses.


指 usually can mean 'refer to'.