Is my irrigation system winterized properly?
The ONLY way to ensure that there is no water trapped in low spots in a sprinkler system is to BLOW it out with compressed air.  Until that is done, there is almost certainly some amount of water trapped and it only takes a small amount to split the buried pipe when it freezes.  Generally sprinkler pipes are buried only a few inches deep and even in moderate climate areas (like Portland) the ground this deep will freeze.  

A properly designed system will have a port where an air compressor can be connected to inject air and if not, you may want to add one to save time later.

Bottom line is that you cannot tell just by looking at the valves if it's been properly winterized or not.