Ok, basically acoustic guitars usually comes only with the bottom strap pin because manufacturers are afraid to add a pin on the base of the neck lest they literally "screw" the whole guitar's sound/neck stablility.
What u can do is to go to most guitar shops and ask them to drill a hole to add the neck pin. Should cost around $5 to $10. This method is quite safe but if u prefer to be 100% safe, then u have to get straps meant for acoustic guitars.
These straps are connected to ur headsock instead of the 2nd strap pin ala electric guitar. If u got an electic strap already, and wish to save money, u can use rafia string or shoelace and tie a knot around ur headsock (between the nut and the 1st tuning machine; under ur strings) and tie the other loop around ur loose end of the strap.