Call Filter - Yellow triangle with !

I have been using the Call Filter for several months and love it.  However, many times a call will come from a caller with only their number as the caller ID, and a Yellow triangle with !, will show and the call will continue ringing.  I usually ignore these calls.  what is the meaning of the triangle, I have interpreted it unofficially as probably spam.  Is this correct?

Re: Call Filter - Yellow triangle with !
Customer Service Rep

Hello Ed3151. We're truly happy to learn that you're enjoying the features of our Call Filter application. The Yellow Triangle does indeed mean that the call is marked as 'Potential Spam'. Here's a link with more facts about the Call Filter feature that may come in handy: Please let us know if you have additional questions.