Arresting a person for holding a blank placard would indeed be Russia-level oppression. The person in question was not arrested, but threatened to be arrested if he wrote a particular phrase on it [1]. Not great at all, but still no cigar.
A man wearing the "Plasticine Action" T-shirt was indeed arrested [2]. That was extra absurd because the protest was against AI-generated animation, not about a political cause.
For holding rhe sign.
The famously authoritarian police threatening arrest for an attempt to hold an EMPTY placard.
Or arresting for a shirt with "Plasticine Action".
Or locking in a prison for several years for zoom call in which they planned nonviolent protest (blocking the motorway).
We could do it for months.