With Wall Street's surge to record highs, the U.S. stock market looks nearly as expensive as ever, and investors are debating whether the lofty valuations are a bearish signal or justified by the technology-heavy market's profit outlook.

Online firearms seller GrabAGun Digital Holdings, with the stock ticker “PEW,” made its market debut after board member and son of the U.S. president, Donald Trump Jr., rang the opening bell at the New York Stock Exchange.