That's still deceiving. I'm betting that it's mass since you cannot have HCl(liquid) at Standard Temperature and Pressure (STP). You'd have to greatly increase the pressure, or greatly decrease the temperature to do so. Here's my logic:
30% by mass = .3g HCl / 1g H2O
MW of HCl = 36.46g
.3g HCl * (1 mol / 36.46g) = .00823 mol HCl
Molarity = mol solute / liter solvent
1g H2O = 1mL H2O (density is 1g/mL)
Thus
Molarity = .00823 mol HCl / 1 mL H2O ; but molarity is mol solute/L solvent so.. by a slight conversion factor (multiply by 1000)
8.23M HCl solution at 30% concentration by mass.
That seems pretty possible since we work with 16M sulfuric and nitric acids at Butler, and they start fuming at that concentration. 8.23M can definitely do some damage.
On a side note, using molarity vs molality to determine whether or not the % concentration is by mass or volume isn't the best method. Almost all concentrations will be in molarity since the only reason why you would need to use molality is analyzing freezing point depressions and boiling point elevations when you add salts to a solvent (for instance, the reason for salting the roads in Indiana, is to decrease the freezing point. Doing so allows the water on the road to become colder before freezing, and stops ice creation). By using molality (where you have only masses, no volumes) you allow the calculation to become temperature independent, since we all know density depends on temperature.
Here's a trick question. How badly would it hurt to pour 100% (by mass) HCl on your hand?