Method base (use mono_compileMethod to get the jitted address) or 0 if it hasn't found any method.
Example A)
local method = mono_findMethodBySignature('PWD', 'PlayerProfileResources', 'UpdateResource', 'PWD.PlayerResourceType,int,PWD.CurrencyAction')
-- to get the jitted address you could now use
local jittedMethod = mono_compileMethod(method)
print(tohex(jittedMethod))
Example B)
local method = mono_findMethodBySignature('PWD.PlayerProfile+IChangeListener', 'UpdateResource', 'PWD.PlayerResourceType,int,int')
-- to get the jitted address you could now use
local jittedMethod = mono_compileMethod(method)
print(tohex(jittedMethod))
Notes
To get a method signature or full qualified name use .NET viewers context menu item