There’s an interesting paper here arguing
that torturing regimes may deliberately sign the Convention Against Torture intending to violate it, in order to signal to domestic opponents that they are so determined to hold on to power they will torture them in spite of the cost they incur for treaty violations. … “Messrs Hollyer and Rosendorff believe the intent [of signing the treaty] is to show how dedicated the regime is to maintaining power, how much it will sacrifice. But there is another possible signal: the regime shows its opponents that it knows international pressure cannot disturb its grip on power in the slightest”. (source)
[A] regime that tortures its opponents and refuses to sign the Convention Against Torture shows that it fears international opprobrium. A regime that tortures its opponents and blithely signs the Convention Against Torture anyway shows that it fears nothing. (source)
This is the proper occasion to link back to an older post of mine on the difference between normative universality and real universality.