Welcome to JOF
Some FW's and TT's have a travel bar(s) that when the slide is closed they are placed between the slide (at top) and the wall (inside of trailer). This keeps the slide "snug" during travel so it doesn't move want to move around. Then before opening the slide one removes the travel bar(s) so the slide will open freely.
Normally when the bars are not in use they are stored in a closet, behind sofa, etc.. Surprised to hear them being utilized on a FW, but then again you have an older model. Is your manual specifically for your model FW, or is it general owners manual? Confirm that the travel bar reference is applicable for your FW.
For piece of mind give Jayco a call at 574-825-5861 (have VIN handy), and they will clarify everything for your model FW.
Most newer RV trailers don't utilize them much anymore, except on some of the smaller units.,
Hope this helps.