I have a dashboard plus sign showing on the speed limit indicator. For instance there will be a plus sign shown next to the "55" speed limit shown on the dashboard panel. What does this mean? The Mercedes mechanic has never seen this. I am in service shop for a loss of power, suspected exhaust regen problem.

 

Vague description. Perhaps a picture if it's possible? Check your owner's manual. I can't imagine the manual not having a description of this warning light. Also, is it on all the time, or at certain times? What color is it? The only + sign on the dash I can think of is the shift indicator for Manual Transmission vehicles, but not all of them show a +, some just a filled in circle, some an arrow.

Is your car at a Mercedes dealership, or with a mechanic that considers himself savvy with MB's or imports? If it is at a dealership I find it odd that they wouldn't know what the light is.
Check the link, it has several images of warning lights. If it's not there, a picture would go a long way. https://www.caasco.com/blog/Automoti...what-they-mean