I am a bit confused by all the people suggesting this is about AutoComplete.
AutoComplete suggests a completion of what you are typing, eg: Google suggesting search phrases.
That is not the same as showing search results.
I think conflating the two and the fact that a search is taking time is going to cause confusion.
I like the idea of a little search icon to indicate that a field triggers a search - so the search is next to those fields to indicate to the user that the field is special.
When a search is being performed, that icon can animate. There is less blink effect if an icon animates than if it pops into view.
Note that if you have such an icon it should also be clickable to trigger the search instantly because some people will try to click it.
One note about searches in general - use timeouts if you want to avoid triggering animations if there's a case your searches will be very fast.
Don't assume searches are always fast. Evernote on Windows drives me crazy because they try to start searching after I type in 2 characters and that's a distinct pause (I have over 17,000 notes and a relatively old laptop that was fast 6 years ago). They trigger this search without delay - I'm a 80wpm typist typing letters in a gestalt burst and it still kicks in regardless of the speed of typing!