You can directly access static classes. The syntax is the same as in PHP.
Note
Direct access to PHP classes is not recommended. This ties the underlying application code structure directly to the presentation, and also complicates template syntax. It is recommended to register plugins which insulate templates from PHP classes/objects. Use at your own discretion. See the Best Practices section of the Smarty website.
Example 217. static class access syntax
{assign var=foo value=myclass::BAR} <--- class constant BAR
{assign var=foo value=myclass::method()} <--- method result
{assign var=foo value=myclass::method1()->method2} <--- method chaining
{assign var=foo value=myclass::$bar} <--- property bar of class myclass
{assign var=foo value=$bar::method} <--- using Smarty variable bar as class name