I say

exclamation4

1. •
   Used for emphasis, or when resuming after diversion or interruption.

   • "Stop! Stop I say!" ordered the professor imperiously. — 1912
2. •
   (UK, old-fashioned) An exclamation of surprise or protest.

   • I say! That's impressive!
   • I say, what is the meaning of this?
3. •
   (UK, old-fashioned) An exclamation used to call someone or attract someone's attention.

   • I say! ... John ... Are you still there? If you're going into town could you get some eggs?
4. •
   (old-fashioned) A traditional introduction to a joke, usually thrice repeated.