LS&MS freight car numbering

Looking at old photos of Lake Shore & Michigan Southern freight cars, I see many that have a letter in front of of behind the numbers. (i.e. "The American Railroad Freight Car" by John White p 323) Can any of you explain if there was a special significance to this numbering system?

On really old photos, the pre-air and Janey coupler era, many cars, LS&MS or other carriers, have the letters "B.T." painted on the lower car sides. Do any of you know what this was an abbreviation for?

How about supplying some examples of the numbering used? Thanks

Here's one LS&MS boxcar with a D in front of the number and two NYC&HR cars with B.T. One has a large B.T. after the number and the other is a small B.T. in the lower right corner. Two of these cars have RED LINE on them. Other cars have BLUE LINE and WHITE LINE. What is the significance of these?

I cannot help with the "D" and "BT" in the car numbers, but this may be helpful:
In 1856 the Merchants Despatch Company started as a fast freight line with box cars marked for the Red Line, Blue Line or White Line. At some point, the company came under control of Cornelius Vanderbilt and thus the New York Central.
The earliest MDT reefers were painted white with a red and blue line along the bottom, a carry-over from the names of the fast freight lines. Later reefers were painted yellow with box car red ends, but in 1947 they returned to using white on the reefers. The last use of the red and blue stripes was on a small batch of these - most did not receive the stripes.
Mike Kmetz

Here is a link for a Railway Equipment Register for June 1901 http://books.google.com/books?id=dxAqAQ ... &q&f=false" onclick="window.open(this.href);return false; Likely the answers are in that document. LS&MS begins on page 38. Jack

Looking at the Equipment Register, the "D" before the number seems to indicate a car "Dedicated" to a service or customer.

I'm wondering if the "B.T." indicted the car had some type of truss rods included in the car bottom framing.