The latest rush of merger and acquisition activity looks likely to unlock a pair of highly coveted single-letter stock symbols on the New York Stock Exchange (search).

Gillette Co. (G) and AT&T Corp. (T) have announced they each will be bought by another Big Board names, Procter & Gamble Co. (PG) and SBC Communications Inc. (SBC), respectively.

If the two mega-takeovers were consummated, Gillette's "G" ticker symbol and AT&T's "T" will be free for the first time in decades for other companies interested in the single-letter market moniker.

Taking a single-letter symbol freed up by a merger last occurred in 1998, when Citigroup took the "C" previously held by Chrysler Corp. After the automobile company merged with Daimler-Benz AG, the combined company took the NYSE symbol "DCX."

As for how symbols are assigned, an NYSE spokesman said it is a collaborative effort between the exchange and listed companies. A company can ask for a preferred symbol, and if that is not available, the exchange will suggest alternatives.

Right now, eight single-letter symbols are unassigned: "H," "I," "J," "M," "P," "U," "W" and "Z". Wall Street lore has it that the NYSE has set aside "I" and "M" for Intel Corp. (INTC) and Microsoft Corp. (MSFT) should the two Nasdaq stalwarts ever decide to transfer. Nasdaq-listed companies have four-letter symbols, or in some cases, five letter symbols.

The NYSE spokesman, citing exchange policy, declined to say if any trading symbols had been reserved for particular companies. He also declined to say if any corporation had expressed interest in unassigned letters.

There also may be another letter opening up in the next few weeks. Sears, Roebuck and Co.'s (S) pending merger with Kmart Holdings Corp. could free up the "S" trading symbol, held by Sears since March 1910. Kmart is listed on Nasdaq Stock Market under the symbol "KMRT."

Spokesmen for these companies either did not immediately know on which market the merged company would list or did not immediately return messages. Under the deal's terms, the surviving corporate entity would be named Sears Holdings Corp.

Gillette has traded on the NYSE since 1927, though not always under the ticker symbol "G." Procter & Gamble joined the NYSE list in 1950. SBC Communications debuted on the Big Board in November 1983 with the break up of the original AT&T that created the so-called Baby Bells (search).

According to the NYSE, AT&T's predecessor company first listed on the exchange in 1901.

Owning a single-letter-symbol stock has been a better-than-average investment over the past three years. Over that time, 11 of the 18 single-letter stocks have outgained the three major stock indexes -- the S&P 500 (up 9.3 percent), Dow Jones industrial average (up 9 percent) and Nasdaq composite (up 15.6 percent).

But AT&T has the second-worst performance over that time among single-letter stocks, losing 38.5 percent of its value.

Over the last 10 years, in fact, AT&T is the only stock on which an investor would have lost money betting on single-letter symbols. It is down 45 percent over the past decade.