Hi,
I would do a quick test too. For some meters you can use an ohm meter to test, but this one might pin and be damaged by most ohm meters, so as Carl suggests use a voltage divider. Make the output voltage around 50mv and connect the meter. If the meter deflects to near the "20" marking, then it's a voltage meter not a current meter, so you need to use an external shunt. If the meter barely moves or not at all, then it has the internal shunt and so you need to keep an eye on the temperature of the meter itself if you use it at currents of say 5 amps or greater.
If it does need a shunt, consider yourself lucky because the ones with internal shunt often burn up if the shunt is not connected properly. 30 amps is a lot of current that you dont play around with because even small resistances will develop a lot of heat. Consider a 0.010 ohm shunt at 30 amps develops 9 watts of heating which is a lot in a small space, so bad connections to the shunt heat up FAST and melt the plastic. Even the right resistor or shunt will develop 2.25 watts at full current, which either has to be external or internal, and a confined 2.25 watts is just as bad as a non confined 10 watts roughly.
This meter does look like it requires an external shunt, but the test will prove or disprove this.
If it turns out that it does need it, buy an actual shunt not a resistor. Shunts are sold as shunts, and state the type of signal such as "50 amps, 75mv" or "50 amps, 50mv", etc. You (may) need a 30 amp 75mv shunt but you dont have to limit yourself to that value either if you really need a different top end on the range.
If you need 60 amps for example, you can get a 60 amp 75mv shunt, which means all the readings will be double what they are marked, so if it reads 30 amps with a measurement then it's really 60 amps. If you use a 15 amp 75mv shunt then when it reads 30 amps it is really 15 amps.
I used a Lafayette 100ma meter for reading 0 to 20 volts for years. Took out the internal 'shunt' resistance (a small coil of wire) and added an external series resistor to calibrate it for 20v full scale. When it read 60ma for example that would mean 12 volts.
If your meter has the internal 'shunt' then the only way you can go is 'up'. You can use another external shunt to increase the current full scale, but you wont be able to go down on the scale (say to 15 amps full scale).
Let us know how you make out with it, and good luck.