My settings were 120 speed, 55 Engraving, and 200 density.  Your settings may vary.  

The sign just fit into the bed of my S1 40w.  but you can reduce or enlarge the project as needed for your item.

Because the original paint was easily wiping off I sprayed a coating of clear gloss over the sign before engraving.  

I then taped over the sign with painters tape to allow easier cleanup.

My settings and the bitmap caused this project to engrave just under 3 hours.  You maybe able to get this done much quicker. 

after removing the painters tape I then cleaned the residue with alcohol and resprayed it with a clear gloss. 

As a Side note:  I made sure to position the project so that the words were engraved on the slats.