Can I use microwave turntable glass plate in convection mode? I bought a Singer SMW25GCQ6 model microwave oven. It has convection and grill features. For baking cakes and for grilling we don't use the glass turntable plate since we thought it could cause the cakes to brown unevenly. 

Is it safe to use the glass turntable in convection mode with the baking to hold the baking cake containers? I'm asking this because there is mode which uses microwave + convection for roasting chicken. So that means the glass turntable should be there and it will work for convection mode as well right?

Then how about grill mode?
Assuming you do not have access to the instruction manual, and/or the manual does not specify whether it is safe to use the glass in convection/grill mode, I would assume not.

Are there any labels and/or writing embossed on the glass?

As I described in this similar question, "regular" soda-lime glass is not heat safe.  Given that the glass was obviously designed for a microwave, it is probably tempered glass, so it can withstand some amount of heat.  Therefore, I would treat it like a Pyrex baking dish and not heat it to over 500°F.  Your microwave's convection mode likely does not get that hot, so you are probably fine with that, but no guarantees.  I would not use the tray in grill mode because even Pyrex is not broiler-safe.