I have a number of tallis katonim that I use. One pair has tzizit which is menupatz. If I use a safety pin to designate that pair, can i wear it on shabbos with the safety pin in an area without an Eruv?The safety pin is only as a simon to tell me which pair it is. Should I remove the safety pin before going outside?
The safety pin should be removed before Shabbos.
The reason for this is that the safety pin is not an integral part of the garment, or a basic part of wearing the garment. The instances in the Gemara and Shulchan Aruch where peripheral items can be carried out are instances of buttons, clips (e.g. to hold up socks), and the like. However, for the safety pin, which has no connection with the garment or wearing it, one must remove the pin before Shabbos.
Instead of the safety pin, I would recommend applying a small amount of dye to the begged, or writing a number on it, whereby it will be easily recognizable.