As the T-shirt sales season hits its summer peak in the UK, so the shirt with a message is once again a best seller. Not since the days of Katharine Hamnett's protest tops which supported the anti-nuclear weapons cause, have printed slogans been so frequently displayed on fashionable chests. But few contemporary T-shirts are overtly political. Instead ranges like those produced by Toby Pimlico for Selfridges of Oxford Street and the House of Fraser departmental chain offer comments on today's lifestyle. Favourites include "Sex and Chocolate" and "Rude when Nude", while single words reported to be selling particularly well are "Freak" and "Pornstar."Meanwhile, the London market for vintage T-shirts continues to expand with mementos of past pop groups particularly sought by connoisseur collectors. They regard such buys as worthwhile investments, even when original Clash or early period Rolling Stones shirts are now changing hands among enthusiasts for upwards of £300. In its turn the vintage T-shirt trade is creating a new niche market within the printwear sector for reproduction classics. Obviously companies like Vintage Trading make the true nature of their products clear to all potential stockists. But the demand for "antique" merchandise is inspiring a number of less than scrupulous printers to pass off their repro garments as the real thing.