I only use Altium Designer. Today I found an arduino due schematic for Eagle PCB Design Software and I saw a symbol I don't know.
What is it, and what is the equivalent in Altium Designer? Is it a directive>>PCB layout in Altium maybe?
I suspect that those are testpoints.
On the schematic, I would use a single-pin connector symbol. Altium may have a suitable schematic symbol in its libraries somewhere, but it may be easier to make your own symbol than finding something suitable in the libraries.
On the PCB, I would use a footprint consisting of a single pad of some convenient size.
You could, of course, simply ignore them, if you wish.