Was the car fully warmed up yet? E34's have an exhaust system that has a lot of mass. Takes a good long time for the exhaust to fully heat up. While it's not fully heated up it's heating up the moisture in the exhaust which is what makes it "smoke" and worries a lot of people that haven't been told that it's normal.
Now if the smoke was blue (burning oil) or black (running rich) you'd have something to worry about.
Considering the weather we've been having around here the last couple of days I'd say that you've just seen the moisture from the exhaust, and that's probably it.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build