Are you talking about in Final Cut Pro? If so, this is in the wrong forum. Please post questions regarding FCP in the proper forum. I've moved this post for you.
As far as your question, they refer to the luminosity of your output image. The exclamation point means that your luminosity levels are too high (according to standard). In a waveform monitor, your highlights would be over 100 IRE (they should be around 90 IRE). So, in order to avoid this, you need to do some image correction. The green checkmark means that your image is broadcast legal.
As far as not getting the warning, in the canvas window, there is a pull down menu that allows you to toggle certain settings. One of them will be luminance warning. Uncheck it, and you shouldn't get the warnings anymore.
Chris
