Listed as unknown symbols by Crawford and others, but correctly identified by Fava.
RRC 412: 59 BCE (so Hersh and Walker and Hollstein)
Notice this depiction uses show two plumbs being used the not four typically used for reconstructions.
Below later images from funerary contexts.
Liv Mariah Yarrow 
[…] marks (and also celebrates Juno Sopita). Some pairs repeat but some see unique to Fabatus. We saw the groma in my last post, but there are other fun examples of Roman technology on this […]