On an original truck they will be parking lights. Unless a previous owner has added a turn signal kit they did not originally come with your truck. Those kits back in the day usually included or were used with something like this.
https://www.flickr.com/photos/advance-design_parts_co/8130552846/in/album-72157631870734114/There was a wide variety of aftermarket versions available and accessory Guide models that could be used. I chose to eliminate these and bought sockets for my original parking lamps to convert them to turn signals.
http://www.classicparts.com/1947-59-Double-Contact-Conversion-Kit/productinfo/47%2D905/
