Global advertising market - FT.com Spring has sprung. Well, so says the advertising industry - and it might even be right. On Thursday, WPP boss Sir Martin Sorrell delivered upbeat forecasts, reporting that group budgets for 2012 show a 4 per cent growth in like-for-like revenues and gross margins. This tallies with soundings from ZenithOptimedia, a media services unit of rival Publicis. It has predicted a 4.7 per cent boost to global ad spend this year (up from 3.5 per cent in 2011), including a 2 per cent improvement in recession-hit western Europe. Even in the UK, there is a whiff of thawing budgets: marketing spend by companies was revised up for two successive quarters in the second half of 2011, according to trade association data. Lex Spring madness? Perhaps not. Part of the 2012 optimism stems from the quadrennial effect. Like leap years, the summer Olympics, European Football Championship, US Presidential election and other polls roll around on a regular ad-boosting basis. Add in the Japanese bounce, post-Fukushima, and ZenithOptimedia reckons these factors combined will bolster ad spend by $7bn, a third of the year-on-year improvement. But a second, more fundamental trend may also be at work. Large multinationals, still wary of financial markets and acquisitions, seem to be investing some additional funds into pushing brands in fast-growing markets and bolstering shares in more turgid ones. Since the start of 2012, this trend has been confirmed by executives at the likes of Kellogg, Unilever, Pepsi and Colgate-Palmolive - although counterparts at Procter & Gamble and L'Oréal have been more cautious.. But investors should be careful. Ad agency shares have enjoyed a strong run over the past six months, and 2013 will be sheared of the "special events" effect. That said, there may selective opportunities: WPP, for example, could probably justify a 13 times forward multiple, in line with peers, compared with the current 11.5. And Spring, while unpredictable, does eventually lead on to summer. E-mail the Lex team in confidence at lex@ft.com