Meaning of small grey circulating arrows on desktop files

I like to keep my major often-used file folders visually atop my desktop for quick access. These folders on my desktop each have a small grey 2-arrow circles showing on the lower right of the desktop file folder icon. Also on my desktop, I keep a few individual files - - and see these small grey 2-arrow circles on the lower right of these (.xlsx, .pdf and .docx). I have 3 other desktop icons which DO NOT have this small grey arrow-circle (these are longstanding-saved .jpg and .pdf manuals). Can anyone explain what these circles-arrows mean and why these more recently used folders and .xlsx and .pdf and .docx files have these symbols (what this arrow-icon means) but my longer-standing .jpg and .pdf do not have these symbols on them?