Would it matter if I mark a Star Realms deck on the front?
No relevant information is conveyed by marking the front of a card. All cards with the same name are totally interchangeable, regardless of whether they are marked.

Logical example

You have two Vipers in your deck. One is marked, and one is not. There are four possible situations.


You draw both Vipers. 

You know that both Vipers are in your hand.

You draw the marked Viper. 

You know that one Viper is in your hand and one is in your deck.
You know that the Viper in your hand is marked. This provides no benefit to you.
You know that the Viper in your deck is unmarked. This provides no benefit to you.

You draw the unmarked Viper. 

You know that one Viper is in your hand and one is in your deck.
You know that the Viper in your hand is unmarked. This provides no benefit to you.
You know that the Viper in your deck is marked. This provides no benefit to you.

You draw no Viper. 

You know that both Vipers are in your deck.



Notice that the relevant information available to you is identical in situations 2 and 3. Only the irrelevant information is different.

Less logical example

Consider Magic: the Gathering along with every other card game that has foil, promo, alternate art, artistically modified (with restrictions), or otherwise "premium" cards. These are all tournament legal. If premium cards compromised the integrity of the game, I think someone would have spoken up by now.