Mike,
For me the first step would be to put safety first. This looks like is would be at least 10 to 15 feet up off the ground. I would stuff the holes with paper and fill them using a UV stable polyester resin and color matched to the existing stone.

Kevin L. Hudson
N-Motion Stone and Tile
(678) 662-0110
> On Jan 4, 2018, at 7:00 PM, Mike Alston <realmikealston@gmail.com> wrote:
>
> Good evening, company is moving signage down on what they believe is a marble backing. I haven't tested it yet to see what the surface is. There will be holes left in the tile that they want filled. I have told them the tiles need to be replaced vs filling the numerous holes left. Has anyone had any experience replacing vertical tiles and what pitfalls may happen, thanks.
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