Oops, I should have also mentioned, these circles are sketched on the drawings. They are not hole features in a part.
Not by default. The usual manual workaround is to add the - sign to a dimension, then create and save a dimension Style and apply that to other dimensions.
Another way is to pre-select all the target dimensions and add the - sign en masse.
Until you specifically establish the X-Y axes on the drawing, I don't believe there are "positive" or "negative" dimension values because there is no establish reference to dictate plus or minus.
Left reading/bottom reading drawings don't imply this.
Without reference axes (a coordinate system reference), all dims are just values that are left/right or up/down of their dimension origins.
Ordinate dim values, like all other dim types, are simply the distance from the chosen dimension origin (it's not a datum, at least not in the image--I know, splitting GD&T hairs) along the ordinate dim entity's alignment vector.
Not that there can't be negative dimension values on drawings. I believe the Hole Table feature can have negative dims, but it establishes an X-Y reference.
Ordinate dims don't have this coord system reference capability,
I'm assuming your drawing doesn't indicate reference axes, but i'm not recommending adding the X-Y reference.
By doing so, you're adding fabrication process instructions, which technically, aren't supposed to be on drawings.
Even without the X-Y reference, specifying negative values adds fab instructions.
Lastly, I try not to hard-code anything, if at all possible, because sooner or later, I'll get bitten.
So, per the above blather, I'm recommending that you don't +/- ordinate dims (outboard of tolerances).
Just my tuppence.
Thanks folks. I was obviously recollecting hole table dimensioning capability, which doesn't apply to this problem for the reasons you have kindly elaborated on.