@ thermos ,

for the full syntax of that special marker naming convention, you can check help at Render to file dialog in Reaper. After you select Output format to DDP, then help button appears.

Also you can employ useful DDP helper written by Karumba, which greatly simplifies that. Because it automatically fills song tiltles according to item names at track 1 and set all the markers according to entered metadata, incl. ISRCs with error verification.
Reaper DDP GUI

I'm not sure how you're familiar with Reaper, but it's Reascript written in Python language. So you'll need to enable Python scripting support in preferences first (Plug-ins/ReaScript), you're at OS X with built-in Python interpreter, so it should work out of box after Reaper restart.
Then you need to open Actions dialog and load that downloaded file as a custom ReaScript. Then you can place it to some toolbar or assign keystroke for its launch.

Michal