Signal Cos. may sell its Mack Truck stake.

The La Jolla-based firm said it filed a shelf registration with the Securities and Exchange Commission covering the possible sale of its remaining 10% stake in Mack Trucks Inc. A spokesman said the filing was “in anticipation of a sale, if warranted by market conditions.” Signal purchased Mack in 1967, but by July, 1983, had sold off about 40% of the truck manufacturer to the French auto maker Renault. In August, 1983, Signal sold off 50% of the company in a public offering at $15 per share but retained 10%, or 3.1 million shares, as a “passive investor.” The firm said it hadn’t yet determined when or how many of its shares would be sold.