Elon Musk tweet about Signal messaging app sent stock with same name flying

The surge in Texas health care company Signal Advance continued on Monday as the stock rose by 438%, after previously gaining 1800% during one 24-hour period.

The catalyst: A Thursday tweet from Tesla CEO Elon Musk that said simply, “Use Signal.” Musk was recommending the encrypted messaging service (an independent 501c3) that competes with Facebook's WhatsApp, but a frenzy ensued in Signal Advance (SIGL) nonetheless that has continued for days.

By the numbers: The company's market cap has risen from around $7 million last week to more than $659 million as of Monday's close, according to FactSet.

The bottom line: Strategists think this may be another sign of the overall mania in stock prices. BofA's chief investment strategist Michael Hartnett notes cynically, extreme asset bubbles have been the "natural end to nihilistic bull markets of [the] past decade."

• This one is unlikely to be different, GMO's Grantham writes. "The combination of timing uncertainty and rapidly accelerating regret on the part of clients means that the career and business risk of fighting the bubble is too great for large commercial enterprises."
• "They can never put their full weight behind bearish advice even if the P/E goes to 65x as it did in Japan."