In anticipation of its 90th birthday on June 16, Vancouver-based restaurant franchisor White Spot has introduced commemorative coins and a limited-edition retro menu that celebrates the burger joint’s roots in BBQ chicken. Executive chef Danny Markowicz has brought back White Spot’s ‘chicken in the straw,’ combining a crispy quarter chicken with creamy coleslaw on a ‘nest’ of Kennebec fries, along with other anniversary items, available until June 15. Then, on June 16, customers at…