Many transistors are printed with 'house codes' that only mean something to the company buying them from Motorola. It's almost impossible to find their real part numbers.
Are you sure it's a transistor? Motorola usually use MJE as the letters in part numbers but sometimes only print the digits so it could be an MJE906 although I can't find any reference to such a device being made. If it's an SCR, they use the letters MCR.
Can you show a photograph or tell us it's approximate dimensions and say whether it has a mounting hole in it or an exposed metal area on one side.
Brian.