Is there any way to show that authors are equal in arxiv names?
There does not appear to be any facility presently in these archives of papers to indicate that contribution of both authors was equal.  (I suspect that this is mostly because it is not actually specified in most papers, so it would rarely be able to be known from reading the papers.)  In the absence of this, the best fall-back position is to specify this explicitly in the paper with a statement of contributions.  Some journals are starting to require this anyway, particularly for research papers submitted by teams of people.  There is no reason that you could not add it into your paper if you wish to specify the contributions of the authors.

In regard to this issue, it is worth noting that, except in a relatively small number of cases, the ordering of authors is generally weak information about the magnitude of their contributions to a paper.  Conventions and interpretation of the significance of authorship order differs by field.  In some fields it would be assumed that earlier authors did the majority of the work, and in other fields there is no such assumption.  The main time when you would infer higher contribution from earlier listing is when you have a paper where the first author is a PhD student at a university, and the later authors are academics in the same department, in which case this is usually a paper where the student has done most of the substantive work and the latter are supervisors who have contributed advice, reviews, etc.  In most other cases it is difficult to infer contributions solely from the ordering of the authors.