From bing interactive sdk. Just delete the line with the custom pin from you pushpinOptions and you will get the default push pin with text.
The error in you code that you pass the pushpinOptions as parameter to map.entities.push method, but the options is a parameter of new Microsoft.Maps.Pushpin method.
var offset = new Microsoft.Maps.Point(0, 5);
var pushpinOptions = { text : '1', visible: true, textOffset: offset};
var pushpin= new Microsoft.Maps.Pushpin(
new Microsoft.Maps.Location(47.6, -122.33),
pushpinOptions);
map.entities.push(pushpin);