Most interruptions are people tossing in a thought or a few sentences - not an entire hijack of your message.

Think about what you were saying at the time you were interrupted. Rather than re-starting at that point, backup to about a sentence BEFORE you were interrupted and re-start by repeating that sentence before continuing your comments.

It’s not only a somewhat subtle reminder that you were interrupted, but it helps the audience get back on track with your message.