They just prefix the function names with what type of RPC it is:
Client - ‘ClientMyFunction’
Server - ‘ServerMyFunction’
Multicast - ‘MultiMyFunction’
With the relevant _Implementation and _Validate suffixes of course 
Oh also forgot, they use OnRep_MyFunction for functions called via variable replication:
UPROPERTY(ReplicatedUsing = OnRep_MyVariable)
var MyVariable;
UFUNCTION()
OnRep_MyVariable()