This style can be used to highlight the unnammed highways.

meta 
{
    title: "Noname";
    description: "Could be a U2 song: highlights where the streets have no name";
    version: "0.1_2012-07-29";
    author: "Yann Coupin";
    
    watch-modified: true;
}

meta[lang=fr]
{
    title: "Sans nom";
    description: "Ça pourrait être une chanson de U2: « Where the streets have no name », surligne les rues sans nom";
}

way[highway][!name]
{
    width: 3;
    dashes: 10,10;
    dashes-background-color: red;
}

Styles_Noname-style.mapcss, Styles_Noname.zip