In my book, Auld, the symbol found on the Dunrobin Pict Stone depicts the presence of a siren and also how to lure her.
What are the tell-tale signs? First, the tuning fork. This denotes the song of the siren. (Though it could also easily be a hair decoration like a pin or decorative comb). Secondly, the iconic mirror and comb of the mermaid. And, finally, although it might seem strange, the sirens are seen with salmon runs.
Unlike mermaids, sirens crave human flesh. They bathe in human blood and use it to stay young (much like myths of witches). Their kind are also known as sea witches.
Interestingly, it does appear that there are two different types of fish depicted here. One is clearly a salmon (likely the Atlantic Salmon found near Scotland). The other might be a Pollock fish. The fish is referred to as a Pollock in North America and the United Kingdom. Also, one nickname for it is Lythe (similar to the Greek river nymph and the river running through Edinburgh-Leith).
The Pollock fish is also reflected in the phonetic pronunciation for the siren found in Inuit legend from the far Northern regions of Alaska-Qalupalik. The Qalupalik is very much like Eve in that it uses energy and blood of humans to try to stay young and immortal. There is also the resemblance in Eve’s ties to cannibalism and human sacrifice.