GM Info layer nearly useless

I'd like to put notes on my map on the GM layer so my players can't see them (obviously), but with the transparency on the GM layer, they're pretty much useless.  In what way is the GM layer useful if I can't put notes on it?   I found  THIS voting thread from a while ago but nothing ever seemed to come from it.

Use bright red big letters.

You can put a box behind text to make it show up better, or use tokens with the text as the name (scales with zoom and has a border on the text). You can also use images of text, or use two contrasting colors slightly offset a few pixels with alt.  Alternatively, you can use a transparent token on the objects layer with an aura only you can see and put text in the bars, link the tokens as representing a notes character, and add abilities that whisper the contents of the bars to you.  I use the GM layer for holding tokens I want to reveal at the right moment. 

I use the GM layer for notes without altering it and I have no issue. Perhaps my maps have better contrast? I don't find it to be difficult to use or read my notes.

A lot of the readability depends on contrast. I experiment with colors and find a different solution on every map. Here's a map where I decided to switch to yellow about halfway through the labeling process. The font is Contrail, which is the heaviest face available.

I use a lot of tokens for various conditions on the GM layer that I can then use macros to display the information out of the bars for various things. But the symbol is what reminds me of traps, treasures, encounters, etc.; with the pertinent information embedded. I used to do it a lot like Keith showed in his post above mine. I'm just lazy and like to recycle the symbol tokens endlessly. It also helps when you throw together adventures on a page quickly.

My Marketplace stuff is similar to Erich's except I suspect my macro stuff in the Bars is a lot more complicated

Other ways the GM layer is useful: Put enemy tokens on the GM layer so they are invisible to the players, even in the Turn Tracker.  This is especially good pre-combat, so the Turn Tracker doesn't display them to the Players so they have no clue how many bad guys there are until they can see them all. Hide map tiles on it.  If there is a secret door that opens and you place a map tile on the GM layer, you can then easily move it to the Map layer to overlay the one that doesn't display the secret door. As the others said, for informational text messages, use big bright letters.  I tend to use Yellow.  Shows up well. Traps.  Like covered pits.  Once discovered, you can move the tile to the map layer so the players see it.