ifs and butts
Since the introduction of the smoking ban in all public buildings wall-mounted ashtrays have become a familiar piece of ‘street furniture’ all over the UK.
The idiom 'No ifs or buts' is used to forestall excuses or objections (which might begin with If or But). The homophone butts (i.e. cigarette ends) might work well here to encourage smokers to use the ashtray, but the local taxi firm who have sponsored it have confused the message by using it to attract potential customers.
Location: exterior of The Hog in Armour pub, Charing Cross, Norwich, Norfolk, UK