Signet shares get a lift from analyst's forecast. (Signet Banking Corp.; Donaldson Lufkin & Jenrette's Thomas K. Brown) (Stocks)

Signet Banking Corp. shares have jumped about 5% since an analyst boosted his 1993 earnings forecast for the bank.

On Monday, the Richmond, Va., bank's stock was ahead 75 cents, to $42.375, in late trading. That was the best gain of the session by a major bank issue.

Last Thursday, Thomas K. Brown of Donaldson, Lufkin & Jenrette Securities Corp. hiked his forecast of 1993 earnings by 35 cents, to $4.40 per share, and reiterated his "very attractive" rating on the stock.

Among Top Performers

In fact, Signet has been among the best performing bank stocks of the year, gaining 90.5%. By comparison, the average price gain for the shares of …