John Deere 3033R, 855 MFWD, 757 ZTrak; IH Cub Cadet 123
NH doesn't seem to publish the Workmaster 105 manual on their site, but looking at the manuals they have there for the other Workmaster, the closest I could find was hydraulic oil pressure warning light.
The droplet symbol is always going to be a fluid, and usually oil. I'm not sure what the inverted flag on the left side of the symbol is supposed to be. Hopefully it's not your oil pressure warning, but you'd think that'd be red and accompanied with some other more obvious indicators.