No recorded arms for Donlon.
None for O'donnellan.
There is something recorded for O'Donellan (county Connaught) derived from the surname of Donelan - Argent an Oak Tree eradicated proper on the sinister side a Slave Sable Chained to the stem Gules. The crest is given as: on a Mount proper a Lion rampant Or, with a motto of 'Omni violenta major' which, in plane[sic] English means 'Too strong for any violence'.
Therefore, it's not a sash but a red chain. ;-))