The main sign of being infected with coin miner malware is an extremal slowness of your system. Since malware miners aim at exploiting your CPU, it makes the system sluggish, as it cannot handle the regular tasks with a proper speed. Coin miner malware leaves only 10-15% of processor power to let the system run, and the user’s tasks are out of the deal.
You can see an auxiliary sign of malware presence - but it is almost the same for any malware process. This one will probably have a dubious name or the name that repeats the one of a system process. However, system processes rarely take over 80% of CPU power - so a process of this quality belongs to malware.