The Honda sign (H sign / H pattern) is a term used to describe the appearance of bilateral sacral insufficiency fractures on a radioisotope bone scan.

Radiographic features
Sacral insufficiency fractures are usually vertically through the sacral alae, parallelling the sacroiliac joint, often with a transverse component - this pattern resembles the capital letter H, leading to the designation of the Honda sign / H sign / H pattern.
https://webcache.googleusercontent.com/search?q=cache:eBVLZQ...

Various patterns of radiotracer uptake have been described, with the so-called “Honda” sign or H-pattern considered diagnostic of SIFs in the correct clinical setting (Fig 5)
http://www.ajnr.org/content/31/2/201
(SIF = Sacral Insufficiency Fracture)



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Note added at 53 mins (2021-06-17 10:26:21 GMT)
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Sacral stress fractures typically develop a characteristic H-shaped pattern, with vertical fractures (in the sagittal plane) through both sacral ala, and a horizontal fracture line through the mid sacrum at the S2 or S3 level. This H pattern is well known on nuclear scans as the “Honda sign” for its resemblance to the auto maker’s insignia.
https://radsource.us/sacral-insufficiency-fractures/