Ligarex is a French product used to strap-clamp low-pressure boots and hoses. It's extensively used in the SM (and other Citroen and French vehicles). It's a flexible metal band and a figure-8 shaped (loosely) "ear" buckle. It relies on crimping of the metal band. It is very low-profile, and not that hard to install.
There are pliers designed to help. Nice, but not essential. They are easily available, made by "OTC", model 4720.
The band comes in various widths. The SM uses 5mm wide bands (primarily? completely?).
It's critical for use inside the suspension cylinder boots for the rear. It can be replaced by hose clamps otherwise. People have also been known to use zip-ties (cable ties). It does look very clean though!
Here's a video by Ligarex on how to install.
Kits of pliers, band, and clasps are easily available but moderately expensive. All available on eBay as well as new.
The bands were also used for CV joints in Plymouth/Chrysler front-wheel drive vehicles. Thus the availability.
Where clearances are tight, the Mirex clamp is used instead. It uses a rotating cotter pin. (Sample and a source) There is also a tool to tighten these.