The signs of age discrimination in these types of layoffs are similar to that in any other layoff:
(a) you are the oldest worker in your group or you are substantially older than most others (you don't necessarily have to be the oldest one);
(b) you have been performing your job well or even better than anyone else, and/or you have been employed with the company for a long time or longer than everyone else in your team;
(c) you are the only one who has been selected for the lay-off, or the employee who have been selected for to be laid off are generally older than others;
(d) the criteria provided to you by the employer as to how they selected who will be laid off either doesn't makes sense or is simply untrue.
If two or more of the above factors are present in your situation during the supposed Covid related lay-off, age discrimination might be at play in your layoff.