Presently, there is no way in ArcaOS to set hard drives to where a RAM disk is automatically recognized and the appropriate drive letter assigned to a specific icon.

BigIcons does allow one to manually set drive letters for RAM drives when Dynamic icons are activated in the Workplace Shell setup icon located in the System Setup folder.

In the BigIcons.txt file found in each theme, look for the lines

;---------------Drive folder icons -- (desktop\computer\drives)
"<WP_DRIVES>"                    "folder_drives_closed.png","folder_drives_open.png"
"<WP_DRIVE_A>"                         "media-floppy_80.png"
"<WP_DRIVE_B>"                         "media-floppy_80.png"
"<WP_DRIVE_S>"                         "media-cd_80.png"
"<WP_DRIVE_T>"                         "media-cd_80.png"
"<LVMREFRESH>"                         "media-LVM_refresh_80.png"
"<PDP_SMARTPFA>"                       "drive-harddisk.png"
"<WP_BOOT>"                            "media-floppy_80.png"

;"<WP_DRIVE_H>"                         "media-ramdisk_80.png"
;"<WP_DRIVE_I>"                         "media-ramdisk_80.png"

The semi-colon is used to comment out these two lines.  To enable the RAM disk icon to be used, just remove the semi-colon.  The default ramdrive letters are H and I.  Change these to the drive letters you use are, or open the ramdisk setup icon in the System Setup folder and change the Ramdrive to H and I.

If you use only one ramdisk, remove the semi-colon statement from only one of the ramdisk statements and change to the ramdisk drive letter you use.

"<WP_DRIVE_X>"                         "media-ramdisk_80.png"