No, you don’t need to sign a cover letter submitted electronically. Hiring managers won’t notice or care that your cover letter isn’t signed.
Simply type out your full name underneath an appropriate cover letter closing, such as “Sincerely,” “Best regards,” or “Respectfully.”
Many cover letter templates use bolded or colored text to help your name stand out at the end of your letter. You can add an electronic signature below your typed name if you like, but it’s not necessary.