Showing the ability to go out and learn something on your own is a big plus. However, don't stop there. It is even better to show how you implemented the technology at your current job (either by request or on your own) and how you managed to solve a problem with it. Making a note that you have a passion (hopefully) for the technology and its application is also a plus.
Selenium has been around longer so there are more jobs (numbers wise) for people that have skills in that area. However, there is a good demand for people with skills in implementing Appium mainly because there are few people that know it and know how to use it well.
I would also like to note that it is VERY important that you also learn the tools and programming skills that go hand in hand with Appium and Selenium. You should be well versed in Unit Test Frameworks (as they apply to automation) and the design patterns that are commonly used (factory, page object). These will be greatly valued as there are many people who can use Selenium (and to a lesser extent Appium) but few who can implement it in a way that is useable in the context of the CI, multi-environment, distributed systems, that more and more companies are using.
But to get back to your question...I would also suggest that you create an automation project and post it on Github to showcase to interviewers/QA Leads/SDETs/Developers that you do know what you are doing. Just make sure that the code is perfect and you have it peer reviewed/proofread!