At the Morris Arboretum, Pennsylvania, US. May 14, 2024. @maf , the tag was barely legible, but the accession number is correct. Couple of other things: whenever I upload pictures to the forum, they always appear less vibrant, don’t know why, but keep it in mind for correct color impressions. The picture with the ruler has messed up colors because of the iridescent blue color, I should have known better…
What a beautiful tree with the branching structure visible in the last picture. Looks to be a slow grower given it was planted 77 years ago! I think it is good for the forum to have an older 'Seigai' with good provenance to be posted here as a reference for debates as to whether it is the same as, or different from, cultivars 'Bonfire' and 'Akaji nishiki'.
A little more information that might be useful: As @maf mentioned, it was planted in 1947. It was acquired from Kingsville Nursery (Kingsville, Maryland) and it is listed in the Arboretum’s Catalogue of Plants as ‘Bonfire Japanese maple’.