Classify as Noise. Monitor only if this escalates into actual trade policy changes with domestic institutional implications. Billboard campaigns by foreign governments are publicity theater, not constitutional events.
This is a Canadian government publicity campaign responding to Trump tariff threats. Despite mechanism='norm_erosion_only', there is no actual constitutional mechanism at play - this is a foreign billboard campaign with zero impact on US constitutional structures. A-score=0 because no US constitutional drivers are triggered (no election interference, no rule of law degradation, no institutional capture). The 0.3 mechanism modifier reflects that 'norm_erosion_only' without actual institutional damage is essentially noise. B-score=21.56 driven by high novelty (foreign government buying billboards in US city is unusual), media-friendliness (visual, easily covered), and moderate intentionality (9/15) as this is deliberate strategic messaging by Canada. However, B-score remains below threshold. This is classic Noise: symbolic international posturing with no constitutional impact, high media appeal but low actual significance.