Is there a universally accepted symbol for the button that shows you where you currently are on a map? The google maps app for smartphone has it.
Short answer: No.
Long answer: There are a few different ones out there (I only bothered to check 3) and some of them offer more functionality than "find me"; for example iOS also uses that button to switch rotation lock modes, Google also uses it to switch rotation lock as well as tilt angle. - It could be argued that these are different buttons and therefor have different icons.
There is No particularly accepted icon for users current location. It's moreover depends on which map/technology user uses. I agree with @Andrew Martin, as he showed those three icons for iOS, Bing and Google.
1. Considering you can target your audience
Since it's hard to tell which is more Universal or easily recognized by users in that case better would be:
Finding your target audience.
Using the same icon used by those Map Provider/Technology. ("same" as I suppose you might be using the API and not developing your own technology)
2. Considering you couldn't know who your audience might be.(Doesn't make much difference)
You can do again two of the follow things:
- Go for Phone Market Share. Based on the number of users around te world you may be able to know, Android being used more so go for Google map icon.
Image below may not be showing updated share of Mobile Market. It's just for rough Idea
Lastly you could go for your custom icon. But this totally depends on how the design is and where you place it.
You could merge iOS and Google Maps Icon
Update: I am just showing you the example, not asking or suggesting you to copy. What i am trying to convey is that you can take the existing as reference.
If you want to use Googles Current Location Icon:
I found that 99% google wouldn't mind you using Current Location Icon. They mind only for following icons/logos related to Map:
Still you want to confirm more. You can ask them for approval here by showing them, where you might be using that icon, if it's copyrighted.