For someone to sign up for a free app they downloaded requires a considerable amount of thought. If a user is forced to sign up without being able to access any of the apps features users are much more likely to uninstall the app after reinstalling. But if a company gives to many or all features to the users then nobody would have a reason to sign up.
The balance is to give users enough of the features to use the apps MVP but offer bonuses for signing up. But the user needs to know what they will get by giving you their information. Must be WORTH signing up for.
Giving the users the option to sign in with social media is great but can make users more nervous if you don't clear up a couple of issues first. You have to let them know that you will not be posting to their Facebook without their permission, another fear users have of giving up their social media is what information you will be getting (Profile Image, Name, Friends List, Likes etc...). So let your users know, be transparent with them.
Also giving your users a "Skip" option if they do not want sign up is crucial. If download a free app but are unable to use it unless you create an account people are much more likely to delete it immediately.
Words of encouragement, or appreciation when they are signing up. People like to be appreciated and reassured of decisions they are making. In the example above I used thank you very much" because the context for someone downloading this app they are most likely planning a trip. If they are planning the trip learning a little bit of the language is a high possibility for that user. So by speaking Dutch to them, I am speaking to their excitement of their upcoming trip they are planning, while thanking/appreciating the user.
Something that has recently become more popular as people are now getting more comfortable with devices is "Show Password". The reason why is people is more comfortable with their passwords. In the early days of when the iPhone was released people were super secretive of hiding their 4-digit lock screen. Nowadays people still have it but are not as secretive as before. Also, plenty of mistakes/typos can be made with a touch keyboard and allow users to see their passwords and adjust it if a mistake was made, reduces frustration, instead of having to retype the whole password. A test I did was if people know they made a mistake when entering a password, they would rather start all the way over instead of correcting the one error they just made if it was hidden. But if it was visible "shown" they would g back and fix the mistake instead of retyping the whole password again.
The lock icon and text is giving the users the peace of mind that their information is safe is so they will continue the signup. Even if the security is the same for a company that didn't have the lock icon, it is for the users, peace of mind (Mobify tip).