The triangle and yellow brake light sign on your BMW 325i is just a symbol that is telling you that there`s something wrong in your car. I go to some forums and I found out that this problem happens when your almost out of gas, it`s a warning. That symbol will appear when you have less than 60 miles of fuel supply in your car. Refill your tank and that symbol will be gone.
Do you also have a small triangle showing with an exclamation point in the center of it in the top right of the lower display? It is telling you to look at your check control system. Push the button on the end of turn signal lever until you get to check control, then use the up and down knob also on that lever until you see the message of what's wrong. It could be front pads, rear pads, or low brake fluid. You can also look at the check control in i-drive, if you have that. Check control is explained in detail in the owner's manual. If you don't have one, you really should get one. Or at least know that you can read it online at