I think the usual symptoms: shortness of breath, dizziness, high heart rate are all possible signs.
Anyone with a mechanical valve should be prepared with the idea of a needed replacement in about 10 years, that's what I recall as the life expectancy of a mechanical valve. New ones may be better, my data/experience is from 7 years ago when I had a mitral valve repaired, a replacement was not necessary for me.
Anyone with a mechanical heart valve, or a repaired one for that matter, should be checked by a cardiologist at least once a year, maybe more often after the valve is 5 years or more old.
Tissue valves have a limited lifespan (10-20 years), but mechanical ones are not prone to structural deterioration. So the chance that your mechanic heart valve fails during your life is minimal.
Younger people, with longer life expectancy, normally get a mechanical valve as older people often get the (pig) tissue valve. Disadvantages of the mechanical valve are that you have to take anticoagulation medicine for the rest of your life and also that you can sometimes hear the clicking sound that the valve makes.