The glass most of us associate with the Martini is, of course, the Y-shaped one – a deco-era motif that’s been patterned out round the world in countless neon bar signs.

One aspect of lovably downtrodden Chinatown dive bar Li Po Cocktail Lounge is looking very fresh these days: Its 70-year-old neon sign, an intricate, six-sided Chinese lantern. Long broken and ...